by Richard Resch

In December 2023, Google announced that Location History would be migrated from its servers to users’ devices, a change that would effectively end the company’s role as the principal recipient of law-enforcement demands for mass location data and render obsolete the centralized database (known internally as “Sensorvault”) that had housed that data. Location History would move to encrypted, on-device storage that Google itself could no longer access. As of July 2025, all Location History data previously stored on Google’s servers was deleted or migrated to on-device storage, and all newly collected Timeline data is stored on-device. In a March 2026 amicus brief filed in Chatrie v. United States, No. 25-112 (U.S.), Google informed the Supreme Court of the United States that it can no longer respond to geofence warrants based on Location History and has objected to more than 3,000 such warrants on constitutional grounds. The case arises from a 2019 Virginia bank-robbery investigation in which police served Google with a geofence warrant, used the company’s multi-step process to work backward from anonymized location points to subscriber information, and ultimately identified Okello Chatrie, who moved to suppress the evidence.

Therefore, Chatrie presents a distinctive problem. The Supreme Court is reviewing the constitutional validity of that geofence search after the en banc Fourth Circuit affirmed the denial of suppression without producing a majority rationale on whether a Fourth Amendment search had occurred. United States v. Chatrie, 136 F.4th 100 (4th Cir. 2025) (en banc) (per curiam). The Court granted review limited to whether execution of the warrant violated the Fourth Amendment, not whether suppression should follow. But it must answer that question in a case involving a surveillance technique whose original Google implementation no longer exists in the form that generated the litigation.

The paradox disappears once you look beyond Google. The specific pipeline is gone. Police can no longer serve a geofence warrant on Google, wait for the company to search its entire Sensorvault of roughly 592 million user accounts, and then work backward from an anonymized list to build a suspect pool. But the underlying model of reverse-location surveillance, the practice of identifying unknown people based on where they were rather than who they are, did not disappear when Google pulled the plug. It migrated.

This cover story documents three mutations of that model, each already generating litigation and each posing constitutional questions that the Chatrie decision alone may not resolve.

The first is the oldest. Tower dumps, court orders compelling cellular carriers to disclose every device connected to a particular cell tower during a specified window, predate geofence warrants by years and have now moved from a supporting role to center stage. The second is the most troubling. Federal agencies are purchasing commercially available location data from the advertising ecosystem to conduct the functional equivalent of geofence searches without any warrant at all. The third is still emerging. Reverse-keyword warrants, AI chatbot prompt searches, and other novel techniques all operate on the same structural logic, searching first and developing suspicion second.

For Criminal Legal News (“CLN”) readers, the stakes are immediate. Anyone whose case involved, or could have involved, a geofence warrant, a tower dump, or location evidence obtained through commercial data purchases has a direct interest in how Chatrie is resolved, especially if the case is still pending on direct review or the issue remains live in postconviction litigation. Suppression, however, has been difficult to obtain in the federal appellate cases that have thus far shaped the doctrine. For example, in United States v. Smith, 110 F.4th 817 (5th Cir. 2024), reh’g en banc denied (5th Cir. Jan. 14, 2025), the U.S. Court of Appeals for the Fifth Circuit concluded that geofence warrants are “general warrants categorically prohibited by the Fourth Amendment” but still affirmed the denial of suppression under the good-faith exception.

The remedial picture is not entirely bleak. In People v. Dawes, No. 19002022 (Cal. Super. Ct. San Francisco Cnty. Sept. 30, 2022), a California trial court granted suppression of geofence evidence, finding that the warrant failed the particularity requirement under both the Fourth Amendment and the California Electronic Communications Privacy Act (“CalECPA”) because it swept in the Location History of “innocent people’s 13 homes” well beyond the burglarized residence. Suppression succeeded in part because the Dawes Court ruled that CalECPA’s suppression remedy did not incorporate the federal good-faith exception, making the officer’s reasonable reliance on the warrant irrelevant. That distinction frames the sharper question for defense practitioners. Suppression is not impossible. The harder problem is why even strong constitutional rulings have so often failed to produce that remedy under the federal exclusionary rule and what it will take to change that calculus.

CLN has covered this story before. Our February 2024 cover story examined thegeofence warrant threat and Google’s initial announcement of its on-device migration. Our October 2024 follow-up analyzed the Fifth Circuit’s landmark Smith decision. This cover story picks up where those left off. It provides the definitive account of where the law stands after the circuit split, the Supreme Court’s certiorari grant, the full briefing, and the April 27, 2026, oral argument in Chatrie. And it maps the mutations that will determine whether the Fourth Amendment’s prohibition on general warrants can keep pace with a surveillance environment that has learned to circumvent judicial oversight.

A Brief Refresher – How the Google Geofence System Worked

Readers who encountered CLN’s February 2024 cover story on geofence warrants will find the mechanics familiar. What follows is a compressed recap of how the system operated before Google’s 2023–2025 migration to on-device storage ended the company’s role as the principal recipient of geofence warrants, described at the level of detail needed to follow the constitutional and practical arguments ahead.

At the center of the geofence warrant apparatus was Google’s Sensorvault, an internal database that stored the location data of users who opted in to Google’s Location History service. Location History was disabled by default, but users were frequently prompted to enable it across multiple apps, and fully deactivating it was, by Google’s own internal admission, deliberately difficult. As the Fifth Circuit recounted in Smith, Google’s own employees acknowledged that deactivating Location History collection, based on Google’s “limited and partially hidden” warnings, was “difficult enough that people won’t figure it out.”

The scale of the resulting database was staggering. As of October 2018, Google estimated that approximately 592 million accounts, roughly one-third of all Google users, had Location History enabled. Once activated, the service logged a device’s location on average every two minutes, drawing on GPS signals, nearby Wi-Fi networks, Bluetooth beacons, and cell towers. The resulting data was considerably more precise than cell-site location information of the kind at issue in Carpenter v. United States, 585 U.S. 296 (2018), capable of locating an individual within approximately 60 feet or less, and in certain circumstances down to three meters. It could even discern elevation, pinpointing the specific floor of a building where a person might be standing.

Google was not the only company to receive geofence warrant requests. As Smith notes, companies including Apple, Lyft, Snapchat, and Uber also received them. But Google was dominant because of the breadth of Sensorvault and because it was, so far as was publicly known, the only company that actually produced responsive data.

When law enforcement obtained a geofence warrant and served it on Google, a three-step process unfolded, which was developed jointly by Google and the Department of Justice’s Computer Crime and Intellectual Property Section in response to the surge of early geofence warrants.

At Step 1, law enforcement specified a geographic area and a time window surrounding the alleged crime. Google then searched its entire Sensorvault, all 592 million accounts, to identify every user whose Location History placed them within the specified boundary during the specified period. Google could not query a subset of its database. Every geofence search required combing through the full repository. The company returned a list of anonymized device identifiers, along with timestamps, latitude and longitude coordinates, geolocation sources, and confidence intervals.

At Step 2, law enforcement reviewed the anonymized list and selected devices of investigative interest. Officers could request additional location data for selected devices beyond the original time and geographic scope, allowing them to track movement patterns and eliminate bystanders. Google imposed no geographic limits on the Step 2 data but generally required law enforcement to narrow the number of devices before expanding the search.

At Step 3, law enforcement directed Google to unmask the anonymized identifiers. Google provided subscriber information, including the account holder’s name and email address, for the devices law enforcement deemed relevant. With that information in hand, investigators could pursue traditional techniques like phone tracking, additional subpoenas, or arrest warrants.

The growth of this practice was explosive. Geofence warrants were virtually unknown before 2018. From 2017 to 2018, requests to Google increased over 1,500%. By 2019, Google was receiving roughly 9,000 geofence requests per year. By 2020, that figure had climbed to approximately 11,500. By 2021, geofence warrants constituted more than 25% of all warrant requests Google received in the U.S. And the technique was not reserved for serious violent crimes. Courts noted that law enforcement had obtained geofence warrants for investigations into stolen pickup trucks and smashed car windows.

The system also produced documented false positives that swept innocent people into criminal investigations. In one widely reported case, Arizona police arrested Jorge Molina, a 23-year-old warehouse worker, on suspicion of murder after a geofence warrant placed his Google account near the scene of a shooting. Molina spent six days in jail before investigators acknowledged that the more likely suspect was Marcos Gaeta – his mother’s former boyfriend, who sometimes drove Molina’s white Honda and who had been using one of Molina’s old cellphones that remained logged into Molina’s Google and social media accounts. Gaeta was later arrested in California in connection with the homicide. The arrest cost Molina his job, his car, and his reputation; he was unable to pass background checks in its aftermath.

This is the infrastructure the Supreme Court has been asked to evaluate in Chatrie. How the circuit courts split over its constitutionality, and how the en banc Fourth Circuit fractured without resolution, is discussed below.

Google Pulls the Plug – The End of Sensorvault, Not the End of Reverse-Location Surveillance

On December 12, 2023, Google Maps product director Marlo McGriff announced a set of changes to the Maps Timeline feature that, once complete, would effectively end the company’s ability to respond to geofence warrants and obsolete the Sensorvault search infrastructure. For users who chose to turn Location History on, Timeline would soon be saved on the user’s device rather than on Google’s servers. Google also announced that, when users first turned on Location History, the default auto-delete setting would be three months instead of 18 months. Users could choose a longer retention period or disable auto-delete altogether, and users who wanted to preserve their Timeline across devices could choose cloud backup, which Google said it would automatically encrypt end-to-end so that no one, including Google, could read it.

The announcement was framed as a privacy enhancement, and in a narrow technical sense it was. But its practical effect on law enforcement was unmistakable. If Google no longer stores Location History on its servers, it cannot search that data. And if it cannot search that data, it cannot respond to geofence warrants.

The migration rolled out gradually over the following year and a half. As noted above, Google’s March 2026 amicus brief confirmed that the migration was complete as of July 2025 and that Google “no longer has the ability to respond to geofence warrants.” The government itself confirmed this understanding. In its brief in opposition to certiorari, the Solicitor General represented that his Office “has been informed that all Location History data was deleted from Google’s Sensorvault database by the end of July 2025” and that Google would be “unable to respond to geofence warrants going forward, except to the extent that Google retains data responsive to specific geofence warrants or geofence preservation requests received before that date.” Sensorvault is gone.

Google’s amicus brief also revealed the scope of the company’s own resistance to geofence warrants during the years Sensorvault remained operational. Google told the Supreme Court that it had objected to over 3,000 geofence warrants on constitutional grounds. For more than 2,500 of those, law enforcement never responded, essentially withdrawing the warrants. In the remaining cases, Google typically reached agreement with law enforcement to narrow or withdraw the request. When officers refused, Google went to court.

The brief described several subsequently unsealed examples of warrants that Google challenged. One covered several search areas spanning 2.5 square miles of San Francisco for a cumulative period of two-and-a-half days. Google objected that the warrant would have exposed the Location History of thousands of users, many of whom “may have been enjoying the privacy of their homes, taking part in protected religious activity in a place of worship, commuting, or engaging in countless other private activities.” The government ultimately withdrew the warrant. In another case, a warrant sought data from seven search areas covering 489 acres in Albuquerque, New Mexico. It would have captured Location History for over 3,000 users, including more than a thousand people attending a funeral service. Google filed a motion to quash, and the government again withdrew the warrant without Google producing any data.

These disclosures serve a dual purpose in Chatrie. They demonstrate to the Supreme Court that the company that built Sensorvault now views the system it created as constitutionally problematic. And they provide concrete illustrations of the kind of overbreadth the Fifth Circuit condemned in Smith when it concluded that geofence warrants are categorically unconstitutional general warrants. Google filed its brief in support of neither party, taking no position on whether the specific warrant in Chatrie satisfied the Fourth Amendment. But the company argued that law enforcement was required to obtain a warrant to access Location History data and that the third-party doctrine should not strip constitutional protection from personal digital records stored on Google’s servers on behalf of users.

The critical question is what Google’s exit means for the broader landscape of reverse-location surveillance.

The short answer is less than it might appear. As noted in the refresher above, no other company maintained a location database approaching Sensorvault’s scale, and it is unlikely that law enforcement can simply replicate the Google model by turning to another technology provider. But litigation over geofence warrants executed before the migration remains pending across multiple jurisdictions, and the constitutional question cannot turn solely on Google’s policy choices. The technique remains logistically viable even if its scope and frequency are diminished.

More importantly, the impossibility of replacing Sensorvault with a single alternative does not mean reverse-location surveillance has ended. It means it has fragmented into the three channels described above: (1) tower dumps, (2) commercially purchased advertising data, and (3) emerging reverse-search techniques. Law enforcement agencies that once served a single geofence warrant on Google can no longer do that. What they can do is obtain functionally similar results through other channels, each raising distinct constitutional questions that a Chatrie ruling alone may not resolve.

Google’s on-device migration thus occupies a paradoxical position in the Chatrie litigation. It strengthens the petitioner’s merits argument to the extent the company that built the tool now maintains that Location History is protected and that overbroad geofence warrants raised serious constitutional concerns. But the migration also narrows the practical reach of any eventual ruling. A defendant-favorable decision would matter directly for cases still pending over warrants executed while Sensorvault was operational, and it would likely help shape the analysis of future geofence-style demands directed to other providers. However, standing alone, it would not resolve the separate constitutional questions raised when agencies obtain comparable location data through commercial brokers rather than through warrants served on providers.

The architecture of the surveillance changed. The underlying problem did not.

The Circuit Split – Fourth Circuit vs. Fifth Circuit

The Supreme Court’s decision to hear Chatrie grew directly from a conflict between two federal circuits that examined the same constitutional question and reached opposite conclusions within weeks of each other. Understanding those decisions, and the fractured en banc proceeding that followed, is essential to appreciating the issues involved.

The Fourth Circuit Panel: No Search Occurred

On July 9, 2024, a divided Fourth Circuit panel affirmed the denial of Okello Chatrie’s motion to suppress geofence evidence but on grounds sharply different from those the U.S. District Court had relied upon. The District Court had concluded that the geofence warrant “plainly” violated the Fourth Amendment, then declined to suppress the evidence under the good-faith exception established in United States v. Leon, 468 U.S. 897 (1984). The panel majority, in an opinion by Judge Richardson joined by Judge Wilkinson, never reached the warrant’s validity. Instead, the panel held that no Fourth Amendment search had occurred at all.

The panel’s reasoning rested on two pillars. First, it concluded that two hours’ worth of Location History data was far less revealing than the seven days of cell-site location information at issue in Carpenter. The panel reasoned that a record of a “single, brief trip” could not expose the kind of comprehensive dossier of physical movements that triggered Carpenter’s protections. United States v. Chatrie, 107 F.4th 319 (4th Cir. 2024). Second, the panel held that the third-party doctrine applied because Location History was voluntarily shared with Google. Unlike cell-site location information, which is generated automatically whenever a phone connects to a network, Location History was “off by default and can be enabled only by a user’s affirmative act.” The panel concluded that because Chatrie knowingly chose to let Google track his movements he assumed the risk that Google might disclose that data to the government.

Judge Wynn dissented. He argued that Location History was more sweeping, granular, and comprehensive than the cell-site data at issue in Carpenter and that the opt-in process was neither meaningfully informed nor truly voluntary.

The Fifth Circuit: Geofence Warrants Are Categorically Unconstitutional

One month later, the Fifth Circuit reached the opposite conclusion. In Smith, the Court concluded that geofence warrants are “general warrants categorically prohibited by the Fourth Amendment.”

The Smith Court found that users of Google’s Location History have a reasonable expectation of privacy in their data. Referencing Carpenter, the Court explained that even a brief snapshot of precise location data can expose sensitive information, “think a visit to ‘the psychiatrist, the plastic surgeon, the abortion clinic, the AIDS treatment center, the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, synagogue or church, [or] the gay bar.’”

On voluntariness, Smith was emphatic. The opt-in process was far from meaningfully informed, the Court determined. Users were “bombarded multiple times with requests to opt in across multiple apps,” while fully deactivating Location History remained “difficult and discouraged.” The court quoted the District Court in Chatrie for the proposition that “a user simply cannot forfeit the protections of the Fourth Amendment for years of precise location information by selecting ‘YES, I’M IN’ at midnight while setting up Google Assistant, even if some text offered warning along the way.”

The Fifth Circuit then addressed whether a geofence warrant, assuming it requires a warrant at all, can satisfy the Fourth Amendment’s requirements of probable cause and particularity. It concluded that the answer is no. The core problem, as the Court framed it, is structural. At Step 1 of the three-step process, Google must search every account in its entire Sensorvault, all 592 million, to identify responsive records. Law enforcement at that point has “no idea who they are looking for, or whether the search will even turn up a result.” This, the Court stated, was “the exact sort of general, exploratory rummaging that the Fourth Amendment was designed to prevent.” In the Fifth Circuit’s view, the “quintessential problem” with geofence warrants is that they do not identify a particular suspect or even establish probable cause to believe that evidence will be found in the database being searched. They identify only a time and place where a person of interest may turn up. Although the results of a geofence warrant might be narrowly tailored once they emerge, the search itself is inherently overbroad at inception because it requires law enforcement, through Google, to “rummage through troves of location data from hundreds of millions of Google users without any description of the particular suspect or suspects to be found.”

Despite this categorical holding, the Fifth Circuit declined to suppress the evidence. Applying Leon, the Court concluded that the officers who obtained the warrant had acted in good faith. The legal environment in 2018, when the warrant was executed, provided no appellate guidance on whether geofence warrants were constitutional. The officers relied on a warrant issued by a detached and neutral magistrate, and their reliance was objectively reasonable given the absence of contrary precedent.

The Fourth Circuit En Banc: Affirmance Without Resolution

The Fourth Circuit vacated its panel decision and reheard Chatrie en banc, with argument on January 30, 2025. On April 30, 2025, the full Court issued a one-line per curiam opinion: “The judgment of the district court is AFFIRMED.” United States v. Chatrie, 136 F.4th 100 (4th Cir. 2025) (en banc) (per curiam).

However, that single sentence was accompanied by eight separate concurrences and one dissent totaling 126 pages. Fourteen of the court’s 15 active judges joined the per curiam. Chief Judge Diaz, in a concurrence, observed that his colleagues held “widely divergent views on the intersection of the Fourth Amendment and the groundbreaking investigative tool at issue here” and ultimately characterized the resulting body of opinions as “a labyrinth of – by my count, nine – advisory opinions, many pointing in different directions.”

A majority of the en banc Court, across several opinions, agreed that the officers in Chatrie acted in good faith and that suppression was therefore unavailable. But the Court did not produce a majority rationale on the threshold search question – the question that had produced the earlier conflict between the vacated Fourth Circuit panel decision and the Fifth Circuit’s decision in Smith – namely, whether the government’s collection of geofence data constitutes a Fourth Amendment search.

Seven judges, in a concurrence authored by Judge Richardson and joined by Judges Wilkinson, Niemeyer, King, Agee, Quattlebaum, and Rushing, would have held that no search occurred, applying the third-party doctrine and distinguishing Carpenter. A separate group of seven judges concluded that a Fourth Amendment search had occurred in some form, though they divided on the reasoning. A concurrence authored by Judge Wynn and joined by Judges Thacker, Harris, Benjamin, and Berner (with Judge Gregory joining except as to footnote 1) would have held that Location History data is protected under Carpenter and that the geofence warrant did constitute a search. A concurrence authored by Judge Berner, joined in relevant part by Judge Heytens, concluded more narrowly that a search occurs at the de-anonymization stage, when the government links location data to a specific individual, placing Heytens on the “search occurred” side of the 7–7 divide even though his own separate concurrence declined to resolve the search question. Chief Judge Diaz expressly declined to reach the question, writing that “judicial modesty sometimes counsels that we not make grand constitutional pronouncements merely because we can.” Judge Gregory, the lone dissenter, would have suppressed the evidence, arguing that the good-faith exception should not apply.

The practical result is that in both Smith and the en banc Chatrie, defendants challenging geofence warrants lost – the former despite a categorical condemnation, the latter without a majority rationale on the merits. The Eleventh Circuit in United States v. Davis, 109 F.4th 1320 (11th Cir. 2024), rejected a geofence challenge on standing grounds. As of this writing, no federal appellate court has ordered suppression of geofence evidence, even where courts have recognized serious constitutional defects in the warrants themselves.

That circuit split triggered Supreme Court review. On January 16, 2026, the Court granted certiorari limited to Question 1 presented: whether the execution of the geofence warrant violated the Fourth Amendment. It did not grant review of the separate exclusionary-rule question. That limitation matters. Even if the Court holds that the warrant violated the Fourth Amendment, Chatrie will not itself resolve whether the good-faith exception bars suppression in other geofence cases. That remedial question will remain for the lower courts where it is properly presented.

Minnesota’s Alternative Path – Protected Data, No Per Se Ban, and a Fatal Step-Two Defect

Twelve days before the Supreme Court heard argument in Chatrie, the Supreme Court of Minnesota charted a materially different course through the geofence problem. In State v. Contreras-Sanchez, No. A22-1579 (Minn. Apr. 15, 2026), the Court held under Article I, Section 10, of the Minnesota Constitution that cellphone users have a reasonable expectation of privacy in location data stored by Google and that law enforcement therefore conducts a search when it accesses that data. Proceeding on state constitutional grounds, the Court declined to decide whether the warrant also satisfied the Fourth Amendment. But it squarely rejected the State’s threshold position that Google-held location data is unprotected simply because it is stored by a third party or first returned in anonymized form. In the Court’s view, the data remained deeply revealing, capable of exposing the “familial, political, professional, religious, and sexual associations” of the person carrying the device, and the supposed voluntariness of Google’s opt-in process was too thin and too opaque to do the constitutional work claimed by the State.

But Contreras-Sanchez did not adopt the Fifth Circuit’s categorical view that geofence warrants are always forbidden general warrants. To the contrary, the Court expressly rejected the claim that geofence warrants are per se unconstitutional. It reasoned that a sufficiently narrow geofence warrant, paired with meaningful safeguards limiting officer discretion at each stage, could in principle satisfy constitutional requirements. The Court also ruled that the warrant application before it was supported by probable cause and did not require a separate probable-cause nexus for every person whose device fell within the geofence. In doing so, it rejected attacks on the warrant’s 65-by-290-foot perimeter and monthlong timeframe, concluding that both were reasonably tailored to the facts of the homicide investigation.

Instead, the defect was located in Step 2. The warrant allowed officers to review the anonymized returns, decide for themselves which device IDs were “relevant,” and then compel Google to provide additional Location History outside the original geofence for 60 minutes before and after the device appeared there, all without returning to a judge for further authorization. The Court determined that such a structure left too much to law enforcement’s discretion and authorized the sort of exploratory rummaging the particularity requirement exists to prevent. The flaw in the warrant was that it failed to supply judicially imposed standards governing which anonymized accounts could be transformed into targets of a broader, more revealing search, according to the Court.

That makes Contreras-Sanchez especially important in the current doctrinal environment. It rejects the all-or-nothing framing that has dominated much of the federal geofence litigation. The Fourth Circuit panel in Chatrie treated Google Location History as unprotected. The Fifth Circuit in Smith treated geofence warrants as categorically forbidden. Minnesota took neither route. It treated access to Google-stored location data as a search, rejected a blanket rule invalidating every geofence warrant, upheld probable cause, and still invalidated the warrant because the narrowing process lacked judicially supplied limits. That is a narrower and, for some courts, potentially more administrable path. It also mirrors the concern that surfaced repeatedly in the Chatrie briefing and oral argument, i.e., whether the constitutional defect lies not simply in the initial collection of anonymized data, but in the later stage when police decide for themselves which accounts deserve expanded scrutiny and eventual identification.

The decision also reinforces the remedial paradox running throughout this area of law. The Minnesota Supreme Court reversed on the merits and held that the warrant violated the state Constitution, but it did not order suppression outright. Instead, it remanded for further proceedings on the good-faith exception and harmless error. So even outside the federal appellate system, the same pattern persists. Courts are increasingly willing to recognize serious constitutional defects in reverse-location searches, but the fight over whether those defects will actually suppress the evidence remains separate, difficult, and intensely consequential.

Chatrie Goes to the Supreme Court – The Briefs and the Battle Lines

The merits briefs reveal not only the immediate stakes for Chatrie himself but a broader contest over whether the Fourth Amendment can adapt to a surveillance technique that inverts the traditional relationship between suspicion and search.

The Petitioner’s Case

Chatrie’s opening merits brief, filed on February 23, 2026, advances two main contentions. First, the brief argues that accessing Chatrie’s Location History was a Fourth Amendment “search” on two independent grounds: (1) because Chatrie held a property interest in his Location History data, which he could review, edit, export, and delete at will, and (2) because he had a reasonable expectation of privacy in his physical movements under Carpenter. He argues that the third-party doctrine does not apply. Location History is not a business record voluntarily provided to Google in the ordinary course of a transaction. It is user-generated data stored in the user’s own account and controlled by the user.

Second, the brief argues that even if a warrant could authorize a geofence search in principle, the warrant here was an unconstitutional general warrant. At Step 1, the warrant authorized the government to search every Google user’s private Location History, millions of accounts, to find every device within 150 meters of a bank robbery during a one-hour window. The government had no idea who it was looking for. And at Steps 2 and 3, law enforcement expanded the search and unmasked subscribers without obtaining any additional warrant, relying on the original geofence authorization for the entire process.

The Government’s Defense

The government’s brief, filed on March 25, 2026, urges the Court to hold that no Fourth Amendment search occurred. Its core argument is that Chatrie lacked a reasonable expectation of privacy in voluntarily disclosed, short-term location information. The government reasons that Location History was an optional setting that Chatrie chose to enable, that only about one-third of Google accountholders enabled it, and that he could request deletion of stored data or pause further collection at any time. The brief distinguishes Carpenter on the ground that cell-site location information is automatically generated as a condition of using a phone, while Location History required several affirmative opt-in steps.

Even if the Court finds that a warrant was required, the government argues that this warrant was constitutionally adequate. Citing Zurcher v. Stanford Daily, 436 U.S. 547 (1978), the government contends that warrants directed at third parties holding evidence that may identify as-yet-unknown witnesses or suspects are well established in Fourth Amendment jurisprudence. The government maintains that the warrant here specified a narrow area (150 meters around the bank) and a narrow time window (one hour), and required Google to return only a minuscule slice of data from its database. Investigators themselves saw only anonymized results, which were to be narrowed between steps. The minimization built into the three-step process was a privacy-protective feature, not evidence of a general warrant, according to the government.

The Amici: A Spectrum of Positions

The amicus filings in Chatrie are unusually rich and varied. They extend the case’s reach beyond the specific warrant at issue and into the broader future of reverse-search surveillance.

On Chatrie’s side, the ACLU, the ACLU of Virginia, the Electronic Frontier Foundation (“EFF”), and the Center on Privacy & Technology at Georgetown Law filed a brief making the most compelling case that geofence warrants are the digital equivalent of the general warrants that triggered the Fourth Amendment’s adoption. The brief drew a direct analogy to Ybarra v. Illinois, 444 U.S. 85 (1979), in which the Court held that police violated the Fourth Amendment by searching bar patrons who happened to be present when officers had probable cause only against the bartender. The brief argued that geofence warrants replicate that constitutional violation at massive scale, turning “innocent bystanders into suspects” based on nothing more than proximity to a crime.

To illustrate the real-world breadth of those searches, the amici cited several examples. In the FBI’s January 6 investigation, Google provided investigators with location data for more than 5,000 devices, and in San Francisco, a single warrant authorized the search of 13 areas, including “thousands of homes, numerous places of worship, multiple schools, many businesses, and highways and other busy roadways,” which resulted in the disclosure of more than 2,600 accounts. The amici also urged the Court to exercise caution in setting a rule based on a 2019 investigation involving technology that no longer exists, warning that future geofence searches directed at companies other than Google “could diverge significantly from this one” and that the record is “silent on how other companies that may hold other kinds of location data manage that information or even what form that information takes.”

The Center for Democracy and Technology, the Surveillance Technology Oversight Project, the Brennan Center for Justice, and Defending Rights & Dissent filed a brief arguing that Carpenter’s reasoning applies with full force to Location History and that the warrant here failed the Fourth Amendment’s particularity requirement. The brief warned that approving geofence warrants would “open the door to the use of other novel reverse warrants” that catalog Americans’ most sensitive associations and activities. Rather than presenting individualized suspicion as the basis for surveillance, geofence warrants “invert the Fourth Amendment” by enabling the government to search first and develop suspicion afterward.

The Knight First Amendment Institute, the Reporters Committee for Freedom of the Press, and the Foundation for Individual Rights and Expression filed a separate brief focusing on First Amendment chilling effects. The brief argued that geofence warrants inherently sweep in constitutionally protected activity because they capture everyone present in a given area, regardless of any connection to the crime being investigated. The brief warned that such a dragnet can expose journalists interviewing confidential sources, protesters attending rallies, and congregants gathered for worship. Should the Court adopt the government’s position, the amici argued, law enforcement investigating any crime could obtain a warrant “authorizing the surveillance of anyone visiting a nearby newsroom, marching in protest on the streets outside, or gathering to pray in the house of worship next door.” The brief urged the Court to apply the Fourth Amendment with “the most scrupulous exactitude” when First Amendment rights are at stake, quoting Stanford v. Texas, 379 U.S. 476 (1965).

The Electronic Privacy Information Center filed a brief on behalf of 14 law-and-technology scholars, arguing that Carpenter provides the proper framework for determining whether geofence searches are Fourth Amendment searches. The brief focused on three factors: (1) the revealing nature of the data, (2) the amount of data searched, and (3) the voluntariness of the disclosure to the third party. The scholars argued that users do not meaningfully consent to police inspection of their location data merely by allowing apps or services to collect it and that the warrant in this case was not sufficiently particularized because it rested only on the time and location of the crime and left officers broad discretion to obtain additional data and identifying information. The brief stops short of saying that every geofence warrant is unconstitutional by design; instead, it argues that this warrant failed Carpenter and the Fourth Amendment’s particularity requirement.

Google’s amicus brief, filed in support of neither party, reinforced the positions described in the “Google Pulls the Plug” section above. Its most significant doctrinal contribution was characterizing Location History as “a personal journal of one’s movements” created with the user’s consent, controlled by the user, and subject to deletion by the user. Consequently, Location History is the user’s personal records rather than Google’s ordinary business records. The brief argued that the third-party doctrine should not strip constitutional protection from personal digital records stored by the company on behalf of users.

On the government’s side, Professor Orin Kerr of Stanford Law School filed an amicus brief proposing a narrow resolution. Kerr argued that Carpenter does not apply because Chatrie voluntarily opted in to Location History and that a properly drawn geofence warrant can satisfy the Fourth Amendment. In his view, the Fourth Amendment does not present “an all or nothing choice between zero protection and absolute protection.” Where the law requires a warrant, it also provides a means to draft a lawful one. Kerr concluded that Step 1 of the warrant in Chatrie was sufficiently narrow in time and space but expressed uncertainty about the constitutionality of Step 2, suggesting that multi-stage warrants raise unresolved particularity concerns. He urged the Court to focus on warrant-drafting standards rather than adopting a categorical prohibition. Whatever path the Court ultimately chooses, the briefing makes clear that even a major ruling in Chatrie will leave important reverse-search questions unresolved.

Chatrie at Oral Argument – What the Justices’ Questions Revealed

The Supreme Court heard oral argument in Chatrie on April 27, 2026. Adam Unikowsky argued for the petitioner; Deputy Solicitor General Eric Feigin argued for the government. The session ran approximately two hours, and it produced several exchanges that bear directly on the constitutional questions discussed in this cover story. What follows is an assessment of the signals that emerged from the bench, informed by the full briefing and the doctrinal landscape described above.

The most important signal is negative rather than positive. The government’s broadest position, that no Fourth Amendment search occurred at all when officers accessed Google Location History, appeared to draw substantial resistance across the bench. Several Justices pressed the government on the implications of treating opt-in cloud-stored location records as wholly unprotected. Justice Sotomayor methodically walked Unikowsky through the consequences of the voluntariness theory, eliciting agreement that if opting in to Location History strips Fourth Amendment protection, the same logic would expose Google Photos, Google Calendar, Google Documents, and email to government access without any search at all. Justice Gorsuch pressed the same point even more sharply from the opposite side of the bench, confronting Feigin with the proposition that under the government’s theory officials could identify everyone at a church, political rally, or abortion clinic without a warrant so long as Google complied. Feigin answered that “effectively” that was the government’s position, a concession that crystallized the danger in the government’s rule. Justice Kagan showed little patience for the government’s attempt to distinguish Carpenter by arguing that cell-site location information is unavoidable while Location History is optional, asking whether the relevant constitutional standard had really become a “nobody-can-live-without-this” test and pressing for a line the government could articulate and defend.

At the same time, the argument did not point cleanly toward a sweeping merits ruling in Chatrie’s favor. Some Justices signaled discomfort with a categorical approach and seemed more interested in narrower paths. Justice Sotomayor, even while probing the defects in the government’s consent theory, remarked that the warrant here was “not a general warrant in a historical sense” because it identified a place, a crime, and a limited time frame. Justice Jackson repeatedly drew attention to the difference between the stages of the Google process, suggesting that Step 1 looked to her less like rummaging through private papers and more like obtaining a list of units in a building, while the more serious constitutional difficulty arose when the government moved from the initial universe of accounts to the narrower groups at Steps 2 and 3 without clear judicially supplied criteria. Those exchanges matter because they suggest that at least some members of the Court may prefer to decide the case by focusing on the lack of standards governing the narrowing process rather than by announcing a Fifth Circuit-style categorical ban on geofence warrants as such.

Justice Barrett appeared especially interested in that narrower, analytically cleaner route. She did not seem drawn to the property-based theory and at one point suggested that a reasonable-expectation-of-privacy analysis might be the more straightforward way to think about the case. But Barrett’s questioning was also damaging to the government. She pressed Feigin on whether the government’s theory would permit tracking into private residences and on whether email, calendar entries, and photographs stored with Google would be different. Feigin ultimately conceded that accessing calendar entries, photos, and email would be a search and acknowledged that warrantless tracking into a private residence would be, at minimum, “a very, very difficult argument” for the government to sustain. Justice Gorsuch immediately observed that this concession was “totally inconsistent” with the government’s broader theory, prompting laughter in the courtroom. That exchange substantially narrowed the doctrinal landscape the government could plausibly defend. It became harder to explain why cloud-stored digital records in the same password-protected account, governed by the same terms of service, are constitutionally protected when they reveal thoughts, communications, and schedules but unprotected when they reveal a record of physical movements.

The voluntariness argument that anchored both the vacated Fourth Circuit panel opinion and the government’s merits brief encountered meaningful skepticism, though not from every Justice in the same way. Chief Justice Roberts initially sounded receptive to the government’s basic premise that users can turn Location History off. But later in the argument he reframed the point in a way more favorable to Chatrie, asking whether protection against surveillance of sensitive locations really depends on people turning off what “many if not most people find is an important service.” Justice Sotomayor reinforced the point by invoking the District Court’s factual findings about the opt-in process, including the now-famous “Yes, I’m in” prompt presented while a user is trying to get a phone working at midnight, and by referencing the evidence that disabling the feature was difficult or opaque. Justice Gorsuch minimized the significance of Google’s terms-of-service language about responding to lawful government requests, observing that such clauses add little because anyone served with a lawful warrant – “a bank, a doctor, a lawyer, anybody” – must comply. The net result was not a bench uniformly hostile to the voluntariness theory but a bench that appeared unwilling to accept voluntariness in the simple, formal way the government proposed.

Justice Alito was the clearest holdout against reaching the merits in any ambitious way. He openly questioned why the Court was hearing the case at all, given that the en banc Fourth Circuit affirmed, the good-faith issue was not granted, and Google’s original Sensorvault system no longer exists. He characterized the petitioner’s request as asking for “basically a law review article” on a subject still only partially developed by precedent. The government encouraged that instinct, reminding the Court that it had warned of the advisory-opinion problem in its brief in opposition and stating that it would be “fine” with a dismissal as improvidently granted. Those exchanges should not be ignored. They are the strongest signals in the transcript that at least some members of the Court were leaning toward to avoiding a broad merits ruling altogether.

Justice Kavanaugh and Justice Jackson pointed toward the most plausible narrowing path if the Court does decide the Fourth Amendment question. Kavanaugh stressed the practical features that make this case less threatening to law enforcement than the government at times suggested. Detective Hylton obtained judicial authorization, used an iterative process, and ended with only three names. And the government conceded under Kavanaugh’s questioning that requiring a warrant in these cases creates no real practical problem because the government already gets warrants. Jackson then picked up the key doctrinal point. If Step 1 is one thing, what criteria governed the move from 19 accounts to 9 and then to 3, and does the Constitution require more particularity or more probable cause at each successive stage? When Jackson asked whether “you need more to get to each step,” she framed a narrow but consequential way to invalidate this warrant without resolving every abstract question raised by reverse searches more broadly. Significantly, Unikowsky accepted that such a ruling would be sufficient, while cautioning that it would be narrow.

For CLN readers, the best reading of the argument is that a majority seems unlikely to embrace the government’s theory in its broadest form, viz., that access to Google Location History is categorically not a Fourth Amendment search. But the argument did not clearly point to a Fifth Circuit-style categorical ban on all geofence warrants either. The more plausible outcomes are narrower. The Court could hold that accessing Location History is a search yet invalidate this warrant specifically because the narrowing and de-anonymization stages lacked sufficient judicially supplied limits. Or it could decide the case even more narrowly on the particularity problems embedded in Steps 2 and 3 while leaving broader questions for another day. The possibility that the Court could dismiss the case as improvidently granted, or issue a decision shaped by the shadow of the good-faith problem even though that issue is not formally before the Court, cannot be dismissed. What the argument did make plain is that the Justices understand this case as a vehicle not just for evaluating a now-defunct Google system, but for deciding whether the Fourth Amendment can police the broader logic of reverse-search surveillance before that logic migrates even further.

The Good-Faith Exception – When a Constitutional Win Doesn’t Suppress the Evidence

For defense practitioners and defendants, the central frustration in the geofence cases is straightforward. Even where federal appellate courts have found or assumed constitutional violations, no Court of Appeals has yet translated that recognition into suppression of the evidence. The doctrinal paths differed – Smith condemned geofence warrants categorically while the en banc Chatrie affirmed without a majority rationale on the merits – but the remedial outcome was the same.

The mechanism is Leon’s good-faith exception. Under that framework, evidence obtained through a defective warrant is not suppressed if the officers who executed it reasonably relied on the magistrate’s authorization. The Supreme Court in Leon identified four circumstances in which good faith will not save a warrant: (1) when the affiant knowingly or recklessly included false information, (2) when the issuing magistrate abandoned judicial neutrality, (3) when the affidavit was so lacking in probable cause that reliance on it was objectively unreasonable, and (4) when the warrant was so facially deficient in particularity that officers could not reasonably presume it to be valid. If none of those conditions is met, the evidence comes in regardless of whether the underlying search violated the Constitution.

In Smith, the Fifth Circuit acknowledged that the defendants’ argument against good-faith reliance on a general warrant was “well taken” but refused to adopt that position given the novelty of a “cutting-edge investigative technique” and the complete absence of appellate authority when the warrant was issued in 2018. The inspectors had consulted with prosecutors, a magistrate approved the warrant, and the Court could not identify conduct that suppression would meaningfully deter.

In the en banc Chatrie, Chief Judge Diaz found the good-faith exception “reason enough to affirm,” ticking through Leon’s four factors and finding none satisfied. Detective Hylton had previously obtained similar geofence warrants, received magistrate approval each time, and could not be faulted for believing the warrant was valid when no court had yet held otherwise.

The result is a paradox that the Brookings Institution has framed bluntly. Defendants are being convicted using evidence that federal courts have expressly said was collected in violation of their constitutional rights. The constitutional holding vindicates the principle. The good-faith exception swallows the remedy.

Three features of the geofence context have made Leon particularly easy for courts to apply. First, novelty. When the warrants in Smith and Chatrie were issued in 2018 and 2019, no federal appellate court had ruled on geofence warrants. Officers had no binding precedent to consult and no judicial guidance to follow. Second, institutional review. In Smith, the inspectors communicated with other law enforcement agencies and the U.S. Attorney’s Office before submitting the warrant, and a magistrate approved it. In Chatrie, Detective Hylton relied on his prior experience obtaining similar geofence warrants that prosecutors and magistrates had approved, and he also obtained magistrate approval for the warrant at issue. Courts treat those layers of institutional review as strong evidence of reasonable reliance. Third, the absence of bad conduct. Neither case involved officers who acted in defiance of known rules or fabricated facts to obtain a warrant. Courts applying Leon have consistently explained that the exclusionary rule exists to deter deliberate misconduct, and where police behavior appears conscientious, the deterrence rationale weakens.

However, for defense practitioners that calculus is shifting. The accumulation of precedent since 2022 has steadily eroded the novelty argument. The Chatrie District Court found a “plain” Fourth Amendment violation and cautioned that good faith “may not carry the day in the future,” speculating that “future geofence warrants may require additional efforts to seek court approval in between steps, or to limit the geographic and temporal information sought.” The Fifth Circuit then declared geofence warrants categorically unconstitutional. The en banc Fourth Circuit fractured across nine opinions without producing a majority rationale. And the Supreme Court granted certiorari on the constitutional question. Taken together, those developments substantially undercut any claim that geofence warrants remain a legally uncharted investigative technique where officers had no guidance to follow. The NACDL’s Fourth Amendment Center has published model motions and practitioner resources designed to help defense counsel press that argument.

The Supreme Court’s ruling in Chatrie could reshape the good-faith analysis in a single term. If the Court holds that geofence warrants violate the Fourth Amendment, the novelty rationale that has sustained good-faith reliance in every federal geofence case to date would lose most of its force. Law enforcement could no longer claim the absence of appellate guidance. Post-decision suppression motions would still require courts to apply Leon to the specific facts and the exclusionary-rule question is not before the Court, so for defendants whose convictions rest on pre-decision geofence evidence the suppression fight will continue in the lower courts. But for every case going forward, a clear Supreme Court holding will strip away the doctrinal shield that has protected geofence evidence from exclusion thus far.

Tower Dumps – The Older Reverse-Location Dragnet Returns to Center Stage

Tower dumps are not new. Long before Google built Sensorvault, law enforcement agencies were compelling cellular carriers to hand over records identifying every device that connected to a particular cell tower during a specified time window. The technique is functionally similar to a geofence warrant. Investigators define a location and a time frame, and the carrier produces data for every user whose phone pinged a nearby tower, regardless of whether any individual user is suspected of anything. The Supreme Court in Carpenter explicitly declined to address the constitutionality of tower dumps, calling its own decision “a narrow one” and reserving the question for future litigation.

That future has arrived. With Google’s Sensorvault dismantled, tower dumps have become a more visible tool in the reverse-location arsenal, and courts in multiple jurisdictions are now evaluating them through the same constitutional framework that has shaped the geofence cases. The results are mixed. Some courts have treated tower dumps as the functional equivalent of reverse-location warrants and rejected them on general-warrant grounds, while others have allowed them when cabined by meaningful narrowing and minimization protocols. Tower dumps now sit squarely within the same constitutional debate as geofence warrants.

The Southern District of Mississippi: Warrant Applications Refused

The most direct application of Smith to tower dumps came in February 2025, when a federal magistrate in the Southern District of Mississippi denied four tower-dump warrant applications in an investigation of a violent street gang suspected of multiple homicides and shootings. In re Four Applications for Search Warrants Seeking Information Associated with Particular Cellular Towers, No. 3:25-cr-38, 2025 WL 603000 (S.D. Miss. Feb. 21, 2025). The government sought data from four carriers for every device that connected to cell towers serving nine crime-scene locations during windows ranging from 10 minutes to one hour each, a combined 880 minutes of coverage across four providers. The government’s own affidavit acknowledged that the warrants “will likely be voluminous and will include the cellular telephone identifiers of otherwise innocent and uninvolved individuals.”

The Court ruled that a tower dump is a search under the Fourth Amendment, applying Carpenter as interpreted by the Fifth Circuit in Smith. It then concluded that the requested warrants failed both the probable cause and particularity requirements. The government had identified seven potential suspects but had not established probable cause to believe that any particular individual committed any specific crime. The warrant applications identified “only a temporal and geographic location where any given user may turn up post-search,” the same deficiency the Fifth Circuit had condemned in geofence warrants. Quoting Smith, the Court reasoned that the tower-dump applications “present the exact sort of ‘general, exploratory rummaging’ that the Fourth Amendment was designed to prevent.”

The opinion was significant for a practical reason. The court refused to issue the warrants rather than issuing them and leaving suppression for later litigation. Defense practitioners should note this as a model. Magistrates can and do reject tower-dump applications at the front end when the constitutional deficiencies are apparent.

The District of Nevada: Unconstitutional But Not Suppressed

Two months later, the District of Nevada reached a similar constitutional conclusion in United States v. Spurlock, 778 F. Supp. 3d 1136 (D. Nev. 2025), a murder-for-hire prosecution. The tower-dump warrant there, served on two carriers, covered cell towers at two locations – where the victims’ bodies were found and where their abandoned vehicle was later recovered – and yielded records on 1,686 unique users from the single carrier that returned data. The Court found that the warrant was “materially indistinguishable from the geofence search warrant foreclosed by Smith” and declared it an unconstitutional general warrant. A warrant that “authorizes the search of anyone who was in a particular area during a particular time range,” the Court wrote, “is too permeating police surveillance.”

But Spurlock followed the now-familiar pattern. Despite finding a constitutional violation, the Court declined to suppress the evidence. The requesting officer had obtained the warrant from a state Superior Court Judge who reviewed the application, found arguable probable cause given the extraordinary circumstances of a double homicide, and limited the warrant’s temporal and geographic scope. The Court cited Smith for the proposition that it “cannot fault law enforcement’s actions considering the novelty of the technique and the dearth of court precedent to follow.” The evidence came in.

New Jersey: Constitutional Limits With Teeth

The New Jersey Appellate Division took a different approach in State v. Bryant, No. A-1399-24, 2025 WL 3481348 (N.J. Super. Ct. App. Div. Dec. 4, 2025), a home-invasion robbery and sexual-assault prosecution. There, law enforcement obtained four tower-dump warrants, and the State ultimately received information from approximately 10,477 cell phone users. The Court held that tower-dump searches are Fourth Amendment searches requiring a warrant supported by probable cause and particularized in the information they seek, grounding its analysis in both the federal Constitution and the New Jersey Constitution’s independent privacy protections. It found the warrants unconstitutional on three grounds: (1) they lacked particularized probable cause as to the thousands of uninvolved subscribers swept in, (2) they were overbroad in the subscriber information demanded (including social-security numbers and dates of birth, a scope the New Jersey Attorney General conceded at oral argument was “problematic”), and (3) they were geographically overbroad, covering more than 20 towers across roughly 193 square miles rather than being tailored to specific cell sites. The Court nevertheless affirmed the denial of suppression on alternative grounds, concluding that information identifying the defendants would have been inevitably discovered or discovered from independent sources.

Importantly, the Court directed the State to delete and not maintain information obtained through the tower-dump warrants regarding innocent third parties once that information was no longer required for, or subject to discovery in, the criminal proceedings. The opinion notes that the State did not dispute that 10,474 users were not involved in the robbery and assault. If the State believes it needs to retain any third-party information beyond the appeal period, it must apply to the court overseeing the criminal matter and obtain an order authorizing retention. This data-deletion requirement provides a concrete remedial framework that defense counsel should invoke in any tower-dump case.

The Northern District of Illinois: Approval With Protocols

Not every court has rejected tower-dump warrants. In a 2023 sex-trafficking investigation involving five linked attacks, a magistrate judge in the Northern District of Illinois approved a tower-dump warrant after requiring the government to adopt three protocols that materially constrained the search. In re Application for Tower Dump Data for a Sex Trafficking Investigation, No. 23 M 87 (N.D. Ill. Feb. 6, 2023). First, the government could seize data only for phone numbers appearing at two or more of the five crime-scene towers, on the theory that overlap across multiple locations substantially increased the probability that the device belonged to a suspect rather than a bystander. Second, the government agreed to take no further investigative steps (including grand-jury subpoenas for subscriber information) on any data that did not meet the overlap requirement. Third, all non-responsive data would be segregated with a law enforcement employee uninvolved in the investigation and could not be accessed by the investigative team without further order of the court.

The Court acknowledged that these protocols were “not bullet-proof” and could still sweep in innocent people whose devices happened to connect to multiple towers. But it concluded that the Fourth Amendment does not demand a scalpel when a warrant is supported by probable cause and constrained by meaningful minimization. The overlap requirement, in particular, converted a dragnet into something closer to a targeted search by requiring a factual basis, connection to multiple crime scenes, before the government could unmask any individual.

The Doctrinal Trajectory

These four decisions confirm that the same doctrinal framework shaping the geofence cases – search, particularity, good faith – is already being applied to tower dumps and with the same remedial frustration. Courts have so far declined to suppress even where they find constitutional violations. But the accumulating precedent from Smith through the Mississippi, Nevada, and New Jersey decisions is building the doctrinal foundation for overcoming that pattern in future cases. The NACDL has published model suppression motions for tower-dump evidence, available through its Fourth Amendment Center, that incorporate these arguments.

The Ad-Tech Pipeline – Buying What You Can’t Warrant

The geofence warrants at issue in Chatrie required the government to apply to a magistrate, describe the area and time period to be searched, and obtain judicial authorization before Google produced any data. Whatever the constitutional deficiencies of those warrants, they at least ran through a court. The most significant mutation of the reverse-location surveillance model dispenses with that step entirely. Federal agencies have discovered that they can purchase commercially available location data harvested from the advertising ecosystem and use it to track individuals without obtaining any warrant at all.

The pipeline works like this. When a smartphone user opens an app that has been granted permission to access location services, the app may transmit the device’s GPS coordinates to advertising networks. This occurs through software development kits (“SDKs”) embedded in the app’s code or through real-time bidding (“RTB”), the automated auction process that serves targeted advertisements. In RTB, the user’s location, device identifier, and other data points are broadcast to hundreds of potential advertisers in milliseconds. That data enters a commercial ecosystem where data brokers aggregate it, package it, and sell it to buyers that include not only marketers but also surveillance contractors and government agencies. As the EFF documented in a March 2026 analysis of the pipeline, the advertising ecosystem effectively converts routine smartphone use into a surveillance infrastructure that the government can access for a fee.

The scale and mechanics of federal purchases came into much sharper focus through a 2024 Privacy Impact Assessment (“PIA”) published by U.S. Customs and Border Protection (“CBP”). The PIA, which 404 Media obtained and reported on in March 2026, disclosed that CBP had procured access to commercial databases containing geolocation data associated with mobile devices’ advertising identifiers from December 2018 through September 2023. During that period, CBP agents queried the data to support what the agency described as targeting, vetting, analysis, and “illicit network discovery.” The PIA confirmed that CBP users conducted two types of searches within the commercial platforms: (1) “location-based searches,” which the document itself described as “geofences” around known locations of law enforcement interest and (2) device-specific searches on known advertising identifiers associated with individuals under investigation.

The parallels to the Sensorvault model are striking. CBP was drawing virtual boundaries around locations and querying a database to identify devices that appeared within those boundaries during a specified period, a technique closely analogous in structure to the reverse-location searches condemned in Smith. The difference is that CBP was accessing commercially aggregated data through vendor platforms rather than compelling a technology company to search its own holdings pursuant to a warrant. The PIA describes that access as contractual use of commercially available data subject to internal rules of behavior. The broader legal proposition, that buying such data falls outside the warrant requirement because the government is purchasing rather than compelling it, is better understood as the position advanced by defenders of the purchase model than as a proposition the PIA itself squarely analyzes.

The PIA itself acknowledged that this arrangement raised “significant legal and privacy issues.” It conceded that the privacy risk of individuals not knowing their data was accessible to CBP through a commercial database was “not mitigated.” It further acknowledged that individuals “may not have realized that commercial vendors collect and sell this kind of sensitive tracking information” and “may not have known how to opt out of this collection.” CBP’s defense was that the commercial vendors had verified that the data they sold was collected from users who consented through apps’ terms of service.

That defense has since come under additional pressure from the Federal Trade Commission (“FTC”). On January 14, 2025, the FTC finalized a consent order against Gravy Analytics and Venntel, one of the brokers publicly linked to the Department of Homeland Security (“DHS”) purchases of location data. The FTC’s complaint alleged that the respondents failed to take reasonable steps to confirm that consumers had consented to the collection, use, and sale of their location data, in violation of Section 5 of the FTC Act. The final order required the respondents to implement a sensitive-location-data program and to adopt measures designed to ensure consumer consent. In re Gravy Analytics, Inc. & Venntel, Inc., Docket No. C-4810 (F.T.C. Jan. 14, 2025).

However, the order’s reach is more limited than it appears. Its definition of “Location Data” excludes data used for security purposes, for national-security purposes conducted by federal agencies or other federal entities, and for a federal law-enforcement response to an imminent risk of death or serious bodily harm. Those carve-outs leave the order’s prohibitions inapplicable to the categories of government access that civil liberties advocates regard as most troubling, though the order does not exempt all government purchases of location data. A routine federal investigation or a state-law-enforcement purchase would not fall within the exclusions.

CBP’s vendor-access evaluation period ended in September 2023, but CBP’s own 2024 privacy assessment says the agency continues to use commercial telemetry data retained from its past use of vendors. As Senator Ron Wyden, Representative Adriano Espaillat, and more than 70 other Democratic members of Congress detailed in a March 3, 2026, letter to the DHS Office of Inspector General (“OIG”), Immigration and Customs Enforcement (“ICE”) has resumed purchasing location data. ICE issued a no-bid contract to surveillance company Penlink in 2025 that included licenses for Webloc, a location-tracking product originally developed by Cobwebs Technologies. Webloc allows agents to draw a virtual boundary around a geographic area and identify devices present within it, using commercially sourced advertising data, functionality that is difficult to distinguish from a geofence search conducted without judicial authorization. The Washington Post reported in January 2026 that ICE’s Webloc subscription enables agents to “geofence” an area using commercial data, while 404 Media documented that Webloc uses commercially sourced location data without warrants.

The Wyden letter also stated that DHS still had not adopted a department-wide policy governing the use of commercially purchased location data, despite a 2023 OIG recommendation. The lawmakers wrote that the OIG’s 2023 review found that CBP, ICE, and the Secret Service had violated federal law through their warrantless purchase and use of location data. They highlighted serious oversight failures such as employees sharing accounts and passwords, supervisors failing to request or review audit logs, and one instance in which a DHS employee misused the data to track coworkers. The OIG’s own public summary framed the findings in somewhat narrower terms, stating that those components did not adhere to privacy policies or develop sufficient policies before procuring and using commercial telemetry data.

The practice extends beyond federal agencies. The EFF’s 2022 investigation of Fog Data Science revealed that the company was selling warrantless mass surveillance capabilities to local law enforcement agencies for under $10,000 per year, using advertising-identifier location data. Fog’s “area search” function was, as the EFF described it, functionally equivalent to a geofence search. An AP and CBS News joint investigation found that Fog Reveal had contracts with nearly two dozen agencies and noted a critical detail for defense practitioners. The tool was “rarely, if ever, mentioned in court records,” raising serious questions about whether its use was being disclosed in discovery.

The constitutional question hanging over all of this is whether Carpenter’s warrant requirement extends to data the government purchases rather than compels. The government’s position has been that the Fourth Amendment is triggered only when the government compels a private party to produce data, not when it purchases data that a private party has independently collected and offered for sale. No appellate court has definitively resolved this question. As a Lawfare analysis observed in 2024, the purchase model may not even constitute “state action” under traditional Fourth Amendment doctrine if the government is merely buying what is freely available on the commercial market.

Defense practitioners should understand why this loophole matters for the Chatrie litigation. A Supreme Court ruling that geofence warrants violate the Fourth Amendment will bind law enforcement when it seeks to compel technology companies to search their databases. It will not, by its own terms, govern the government’s purchase of functionally equivalent location data from commercial brokers. If an agency can buy the same information it would otherwise need a warrant to obtain, the constitutional holding is reduced to a formalism. The Fourth Amendment protects against compelled disclosure but not against purchased access to the same data.

The distinctions between ad-tech data and Sensorvault are real and should not be flattened. Commercially purchased location data is often less precise, less comprehensive, and less reliable than the GPS-enriched data Google stored in Sensorvault. No single data broker has anything approaching the 592-million-account coverage that Google maintained. The CBP PIA itself confirmed that “no single commercial telemetry data vendor has comprehensive coverage of all available cell phone geolocation data globally.” And the data is typically delayed by 18 to 24 hours, making it unsuitable for real-time surveillance. These are meaningful differences, and defense practitioners should not overstate the equivalence when litigating challenges to purchased data.

But the structural problem remains. The government can define a geographic area and a time window, query a commercial database, and obtain a list of devices that were present, all without a warrant, without a magistrate, and without the safeguards courts require for compelled geofence searches. That is reverse-location surveillance in functional terms, even if the Fourth Amendment question for purchased data remains unresolved. And unless courts or Congress closes the purchase loophole, a victory in Chatrie may prove hollow.

Beyond Location – Reverse-Keyword Warrants, AI Prompt Searches, and Other Emerging Dragnets

Tower dumps and ad-tech purchases are the most developed mutations of the reverse-location model, but they are not the last. A newer class of reverse-search techniques has begun appearing in court filings and amicus briefs, each operating on the same structural logic as geofence warrants. That is, the government searches first and develops suspicion second. The public case law on these tools is thinner and less settled than the tower-dump and data-broker doctrines examined above. But they have earned a place in this story for a specific reason. The Chatrie amici themselves are warning the Supreme Court about them, arguing that the constitutional framework the Court adopts will shape not only the future of geofence warrants but the entire family of reverse-search surveillance.

Reverse-Keyword Warrants

The most doctrinally developed parallel is the reverse-keyword warrant. Where a geofence warrant asks a technology company to identify every user present in a geographic area during a time window, a reverse-keyword warrant asks a search engine to identify every user who searched for a particular term during a specified period. The investigative logic is identical. Investigators start with a fact that may be connected to a crime, query a massive database, and work backward from the results to generate a suspect pool.

The Colorado Supreme Court addressed this technique in People v. Seymour, 536 P.3d 1260 (Colo. 2023), the first state supreme court to rule on the constitutionality of a reverse-keyword warrant. Investigators in a fatal arson case obtained warrants directing Google to identify all users who had searched for the address of the fire in the two weeks before it occurred. Google’s staged process, similar to the geofence three-step model, returned five Colorado IP addresses. One led to the defendant. The Court concluded that the defendant had a constitutionally protected privacy interest in his search history under the Colorado Constitution and that reverse-keyword warrants implicate the right to freedom of expression, requiring that constitutional protections be applied with “scrupulous exactitude.” The Court found the warrant adequately particularized but assumed without deciding that it lacked individualized probable cause. It nevertheless declined to suppress the evidence under the good-faith exception.

Seymour did not condemn reverse-keyword warrants categorically. The Court wrote that its “finding of good faith today neither condones nor condemns all such warrants in the future.” But the decision established that reverse-keyword searches are Fourth Amendment events requiring judicial scrutiny, not a routine investigative tool exempt from constitutional constraint.

The Pennsylvania Supreme Court reached a different result two years later. In Commonwealth v. Kurtz, 348 A.3d 133 (Pa. 2025), the Court affirmed the denial of suppression but in a fractured decision that produced no majority rationale. A three-justice plurality opinion announcing the judgment concluded that the “average search engine user” lacks “an expectation of privacy in the records generated” by “general, unprotected internet searches.” The plurality distinguished Carpenter on voluntariness grounds, reasoning that unlike cellphone users who “cannot avoid creation of a data trail,” internet users can “avoid or minimize the creation of such records” by using alternative methods. Because the plurality found no protected privacy interest, it did not reach the defendant’s probable-cause challenge.

Three other justices concurred in the result on narrower grounds. Chief Justice Todd, joined by Justices Mundy and McCaffery, would have avoided the constitutional question and affirmed because the warrant was supported by probable cause. Justice Mundy separately added that, if the constitutional issue had to be reached, she would agree with the plurality that users lack an expectation of privacy in general, unprotected searches. The absence of a majority rationale limits the decision’s precedential force but does not diminish its practical significance. The warrant was upheld, and the technique was not invalidated. The CRS Report treats Seymour and Kurtz as divergent authorities within the same doctrinal family, and the tension between them will likely require further resolution as reverse-keyword warrants proliferate.

The Brennan Center’s Warning: AI Chatbots, Reverse-IP Warrants, and Content-Based Dragnets

The Brennan Center for Justice and the Center for Democracy and Technology used their Chatrie amicus brief to argue that the Court’s ruling will reach well beyond geofence warrants. The brief warned that permitting reverse searches “could usher in a broad new class of so-called ‘reverse searches’ and digital dragnets where not only our actions and associations, but our very curiosities and thoughts are vulnerable to government surveillance without individualized suspicion.”

The brief identified three emerging techniques that follow the reverse-search template. First, reverse warrants for AI chatbot prompts. Despite the novelty of AI chatbot services, the brief noted, the use of reverse warrants for ChatGPT prompts has already been publicly documented, with DHS reportedly ordering OpenAI to share user data. Users’ prompts to AI chatbots can be “far more detailed and revealing” than traditional search queries, the brief argued, because they are designed to facilitate an ongoing dialogue that may reflect “the user’s most intimate thoughts and ideas.”

Second, reverse internet protocol warrants, which compel platforms to identify all users who visited a specific web page or viewed a particular video. The brief cited reports of courts permitting warrants requesting the identities of all viewers of specific YouTube videos, potentially unmasking hundreds or thousands of individuals.

Third, the brief warned more broadly that content-based reverse searches, those targeting what a person is “reading, watching, asking, or thinking,” are “uniquely dangerous” because they threaten to chill the exercise of First Amendment rights and “undermine anonymity” in thought and expression.

The ACLU, EFF, and Georgetown Law’s Center on Privacy & Technology reinforced this concern in their separate brief, urging the Court to cabin any ruling to the facts in the record and warning, as discussed in the amici section above, that future reverse-location searches directed at other companies may diverge significantly from Google’s model.

What This Means for the Doctrinal Landscape

These emerging tools do not yet have the volume of litigation that tower dumps and geofence warrants have generated. Seymour and Kurtz are the only state supreme court decisions on reverse-keyword warrants as of this writing. AI chatbot warrants and reverse-IP warrants have barely entered the public record. But the significance of these developments lies less in their current doctrinal depth than in the forum where they are being raised. The amici in Chatrie are telling the Supreme Court, in filed briefs, that whatever rule the Court announces will be applied by analogy to reverse-keyword warrants, AI-prompt searches, and content-based surveillance dragnets. The mutation thesis is not speculation. It is being argued to the nine Justices who will decide Chatrie.

For defense practitioners, the practical implication is forward-looking. The constitutional framework that the Court establishes in Chatrie, whether it emphasizes the general-warrant prohibition, Carpenter’s expectation-of-privacy analysis, or particularity requirements for multi-step warrants, will supply the vocabulary for challenges to every reverse-search technique that follows. Counsel who encounter reverse-keyword evidence, location data purchased from brokers, or any other form of reverse-search surveillance should frame their challenges in terms of the Chatrie framework from the outset, because the arguments being advanced in Chatrie are already being invoked by analogy in the emerging reverse-search cases and briefs.

The Legislative Response – Partial State Limits, Federal Loopholes

Courts are not the only institutions grappling with reverse-search surveillance. State legislatures have begun enacting restrictions on geofence and reverse-keyword warrants, and several federal proposals aim to close the data-broker purchase loophole. But the legislative environment, like the case law, is a patchwork. The protections that exist are real. The gaps they leave are structural.

Utah has gone furthest. In 2023, the state enacted a law requiring law enforcement to obtain a search warrant before accessing geofence data, codified at Utah Code § 77-23f-102. In 2025, the legislature extended those protections to reverse-keyword warrants through H.B. 273, which added § 77-23f-102.2. Both measures passed unanimously in both chambers. Utah’s framework is the most complete state-level response to date, covering the two most prominent forms of reverse-warrant surveillance under a single statutory scheme.

New York has pursued a broader prohibition. Senate Bill 404, introduced in the 2025–2026 legislative session, would prohibit reverse-location and reverse-keyword court orders, bar New York government entities from seeking or using information obtained through such orders, and provide that persons and entities in New York are not obligated to comply with covered orders issued by New York or other states. Earlier versions of this proposal attracted unusual corporate support. As the EFF documented in 2022, Google, Microsoft, and Yahoo publicly endorsed the predecessor New York bill through the Reform Government Surveillance coalition, a consortium of technology companies that rarely takes positions on state legislation. That earlier support remains significant because it placed companies that receive reverse-search demands on the same side as the civil-liberties organizations challenging them. The bill had not been enacted as of this writing.

California considered an even more aggressive approach. Assembly Bill 793, introduced in the 2023–2024 session, would have prohibited both state law enforcement agencies and California corporations from complying with reverse warrants, including those issued by courts in other states. The bill’s dual prohibition was designed to prevent the circumvention problem that limits state-only bans. If California police cannot obtain a geofence warrant but a federal agency or an out-of-state department can, the prohibition protects only against the least likely source of the demand. AB 793 did not advance to enactment.

The CRS Report identifies additional proposals in Vermont, Missouri, and Delaware, confirming that legislative interest is spreading but has not yet produced a national framework. The state proposals vary in scope. Some regulate only government entities, while others, like New York’s S.404 and California’s AB 793, also reach private compliance. But even the broader state measures cannot bind federal agencies operating within the state’s borders.

That jurisdictional limitation is the core structural problem with state-level responses. Utah’s law does not ban geofence warrants. It regulates them by requiring a warrant and imposing specified procedures, and the state later adopted a similar warrant-and-procedure framework for reverse-keyword searches. But a state statute of that kind still cannot create a national rule. It cannot by itself govern federal agencies, and it cannot eliminate the government’s ability to obtain functionally similar data through other channels, including commercial purchases. State legislation can meaningfully constrain state and local practice, but it cannot by itself close the federal purchase loophole or establish uniform nationwide limits on reverse searches.

At the federal level, the gap is wider. The leading legislative response remains the Fourth Amendment Is Not For Sale Act, a bipartisan proposal that would prohibit law enforcement and intelligence agencies from purchasing certain sensitive information from third-party sellers, including geolocation information and communications-related data protected by the Electronic Communications Privacy Act of 1986. The 118th Congress version, H.R. 4639, passed the House in 2024 but was not enacted. By March 2026, however, major civil-liberties advocates were still identifying the Fourth Amendment Is Not For Sale Act, or similar legislation, as the principal federal solution to the data-broker loophole.

Congress did pass the Protecting Americans’ Data from Foreign Adversaries Act (“PADFAA”), which restricts data brokers from selling Americans’ data to foreign adversaries. In February 2026, the FTC reminded data brokers of their obligations under the new law. But PADFAA addresses a different problem. It restricts sales to hostile foreign governments while leaving entirely untouched the domestic law enforcement purchases that civil liberties advocates find most concerning. An FBI director can confirm, as FBI Director Kash Patel did in congressional testimony reported by FedScoop in March 2026, that the Department of Justice purchases commercially available data for law enforcement operations, and no federal statute prohibits the practice.

The Stored Communications Act (“SCA”) presents a related gap. As a Lawfare analysis has argued, the SCA may not provide statutory authorization for reverse searches at all, because the statute was designed to govern requests for records of identified users, not dragnet queries seeking to identify unknown individuals from a mass database. The analysis proposed a new Section 2703A that would ban reverse searches by default while narrowly permitting limited categories and imposing heightened safeguards. That proposal is no longer purely academic. On March 12, 2026, lawmakers introduced the Government Surveillance Reform Act of 2026, which would add a new 18 U.S.C. § 2703A governing disclosure to state and local departments and agencies.

For CLN readers, the practical takeaway is that legislative protections cannot substitute for constitutional arguments. Defense practitioners in Utah may be able to invoke the state’s statutory warrant-and-procedure requirements when challenging reverse-search evidence obtained by Utah law enforcement. Practitioners everywhere else will generally have to rely on the Fourth Amendment, Carpenter, and whatever framework the Supreme Court establishes in Chatrie. But even in Utah, the statute does not solve the larger problem of federal investigations or the government’s purchase of functionally similar data from commercial brokers. The constitutional claim remains the primary tool and for most defendants the only tool available.

Practical Defense Implications – How to Challenge Reverse-Search Evidence Now

The preceding discussion documented a constitutional picture in flux – a circuit split on geofence warrants awaiting Supreme Court resolution, tower-dump litigation spreading through federal and state courts, a data-broker purchase pipeline operating outside judicial oversight, and emerging reverse-search techniques being flagged to the Justices in real time. For defense practitioners and pro se defendants, the question is what to do with all of it. The following discussion translates the doctrinal developments into concrete strategies for challenging reverse-location evidence.

Framing the Suppression Motion

Any suppression motion challenging geofence evidence should begin with Carpenter’s core holding: individuals have a reasonable expectation of privacy in the record of their physical movements, and the government must obtain a warrant based on probable cause before accessing that data. From there, the motion should build on Smith’s categorical holding that geofence warrants are “general warrants categorically prohibited by the Fourth Amendment” because they require searching the accounts of hundreds of millions of users without particularized suspicion directed at any individual.

If the Supreme Court has ruled in Chatrie by the time the motion is filed, the Court’s holding becomes the controlling framework. A categorical prohibition provides the strongest basis for suppression. A case-specific ruling requires the practitioner to litigate the adequacy of the particular warrant on its facts, focusing on the geographic scope, temporal window, minimization procedures, and whether additional judicial authorization was obtained at each step. A warrant-drafting-standards approach, if the Court adopts one, requires detailed comparison between the warrant at issue and the standards the Court announces.

Regardless of the Court’s approach, practitioners should argue in the alternative. Even if the Court does not adopt a categorical ban, the specific warrant in the client’s case may fail on its own terms. Was the geofenced area unreasonably large? Did it encompass homes, churches, medical facilities, or other sensitive locations? Were Steps 2 and 3 conducted without returning to a magistrate? Did law enforcement expand the temporal or geographic scope beyond what the original warrant authorized? Each of these deficiencies provides an independent basis for suppression.

The recent Minnesota Supreme Court decision, discussed above, also supplies a useful noncategorical model for suppression briefing. In Contreras-Sanchez, the Court held that users have a reasonable expectation of privacy in Google-stored location data, rejected the claim that geofence warrants are per se unconstitutional general warrants, upheld probable cause, and nevertheless concluded that the warrant failed because Step 2 gave officers unchecked discretion to decide which anonymized device IDs were “relevant” and to obtain expanded location history without returning to a magistrate. For practitioners litigating in courts unwilling to adopt a blanket prohibition, that is a useful path. The argument is that this warrant failed because it delegated the crucial narrowing decision to law enforcement rather than the judge. Contreras-Sanchez did not itself order suppression, remanding instead for further proceedings on good faith and harmless error. But as a merits blueprint for attacking multi-step reverse-location warrants, it gives defense counsel a concrete and more administrable alternative to the all-or-nothing positions that have dominated the federal cases.

Challenging Tower-Dump Evidence

Tower-dump challenges should be framed using the same general-warrant analysis. As the Mississippi and Nevada decisions discussed earlier, federal courts have already applied Smith’s reasoning directly to tower dumps. The argument is that a tower dump, like a geofence warrant, sweeps in location data from hundreds or thousands of individuals who are not suspected of any crime, rendering the warrant an unconstitutional general search.

Practitioners should also invoke the New Jersey framework from Bryant, which requires tower-dump warrants to be particularized in the information they seek and mandates the deletion of data concerning uninvolved third parties once the investigation concludes. Even if the court does not suppress the evidence, a Bryant-style ruling creates enforceable limits on the government’s retention and use of bystander data. The Northern District of Illinois opinion approving a tower-dump warrant only with overlap and minimization protocols offers another model. Practitioners can argue that any tower-dump warrant lacking comparable safeguards fails the particularity requirement.

NACDL’s Fourth Amendment Center has made the tower-dump suppression motion filed in United States v. Pendergrass, No. 1:17-cr-315 (N.D. Ga. Feb. 3, 2019), available as a practitioner resource. The motion predates Smith, so practitioners adapting it should layer in Smith’s categorical holding and the post-Smith tower-dump decisions discussed above.

Investigating Whether Location Evidence Was Purchased

The data-broker pipeline creates a distinct challenge. Defendants may not know how the government obtained location evidence against them. When location data is purchased from a commercial broker rather than compelled from a carrier or technology company through a warrant, the acquisition may never appear in court records. The AP’s investigation of Fog Data Science found that the tool was “rarely, if ever, mentioned in court records,” raising the possibility that location evidence derived from purchased data is being introduced without disclosure of its source.

Practitioners should pursue several avenues to investigate this possibility. Discovery requests should specifically ask whether any location data used in the investigation was obtained through commercial purchase rather than through legal process directed to a carrier or platform, and if so, from which vendor, under what contractual terms, and pursuant to what asserted legal authority. In federal cases, Rule 16 provides a direct basis for seeking documents and objects material to preparing the defense. Brady provides an additional basis for disclosure when the withheld information is favorable to the defense and material to the outcome, though practitioners should be precise in invoking it; courts will not treat every issue bearing on a suppression argument as Brady material. Public-records requests and FOIA requests may also help uncover vendor contracts, policies, and procurement records relevant to the provenance of the evidence, but they are not a substitute for criminal discovery.

The legal significance of the purchase-versus-warrant distinction is direct. If location evidence was obtained through a warrant, the suppression analysis turns on the warrant’s constitutional adequacy under Carpenter, Smith, and Chatrie. If the evidence was purchased without a warrant, the threshold question is whether Carpenter’s warrant requirement applies to purchased data at all, a question no appellate court has definitively resolved as of this writing. Defense counsel should argue that the functional equivalence between purchased and compelled location data means Carpenter’s protections apply regardless of the acquisition method. The government’s argument that the Fourth Amendment does not reach commercial purchases should be challenged head-on, because accepting that argument would allow the government to circumvent Carpenter entirely by buying what it cannot constitutionally compel.

Overcoming the Good-Faith Exception

As discussed above, the novelty rationale that has sustained Leon reliance in every federal geofence case is eroding with each new decision. Practitioners challenging evidence obtained after August 2024 should argue that Smith, the en banc Chatrie fracture, and the Supreme Court’s certiorari grant have put law enforcement on notice that the constitutional question is no longer novel or obscure, substantially undercutting any claim of reasonable reliance.

Raising First Amendment Chilling-Effect Arguments

Where the geofence or reverse-location search swept in constitutionally protected activity, practitioners should raise First Amendment arguments alongside the Fourth Amendment challenge, drawing on the Knight First Amendment Institute amicus brief discussed above. The legal standard comes from Stanford, which instructed that warrant particularity must be “accorded the most scrupulous exactitude” where First Amendment rights are at stake. Practitioners should invoke this standard when the geofenced area included places of worship, protest sites, newsrooms, political campaign offices, union halls, or medical facilities and argue that a warrant sweeping in data from constitutionally protected locations demands heightened particularity and that the absence of such protection renders the warrant constitutionally deficient.

Practitioner Resources

The NACDL’s Fourth Amendment Center maintains the most comprehensive collection of practitioner tools for reverse-warrant litigation. Its geofence warrants page includes a primer on geofence warrant mechanics and strategies for challenging them, model suppression motions, sample discovery requests, and links to key case documents. Its reverse search warrants landing page covers both geofence and keyword warrants and includes webinar recordings and litigation updates. The CRS Report R48852, published in February 2026, provides the most current neutral synthesis of the doctrinal landscape and is a useful reference for practitioners who need to brief courts on the state of the law across multiple jurisdictions.

The Constitutional Stakes Beyond Chatrie

The geofence warrant that Detective Hylton obtained in 2019 will produce the Supreme Court’s first ruling on reverse-location surveillance. Whatever ground the Court chooses, its reasoning will supply the doctrinal framework lower courts use to evaluate geofence warrants going forward and will likely inform the Fourth Amendment treatment of related reverse-search techniques.

But the ruling will not resolve the problem this cover story has documented. The specific Google pipeline no longer exists. If the story ended there, Chatrie would be a case about yesterday’s technology. It does not end there. As the preceding discussion has shown, tower dumps, commercially purchased advertising data, and emerging reverse-search techniques have fragmented the surveillance model into channels that a single Supreme Court decision cannot fully address. The mutations are not hypothetical. They are documented in government privacy assessments, FTC enforcement orders, congressional oversight letters, and federal court opinions, and they share a structural feature. Each allows the government to search first and develop suspicion second.

For CLN readers, the takeaway is that the fight over reverse-location surveillance will not end when the Court issues its opinion. A favorable ruling in Chatrie will provide essential doctrinal tools, giving defense practitioners a framework for challenging geofence warrants, tower dumps, and future reverse-search techniques that courts or legislatures have not yet squarely addressed. Such a ruling would strengthen merits challenges, materially weaken the good-faith arguments that have thus far shielded geofence evidence from exclusion, and signal that the Fourth Amendment applies with full force to digital dragnet surveillance.

What it will not do, by itself, is close the purchase loophole, compel Congress to enact the Fourth Amendment Is Not For Sale Act, or directly resolve whether the warrant requirement applies to data the government buys on the open market. Those fights require separate litigation, separate legislation, and sustained attention from the defense bar.

The Fourth Amendment’s prohibition on general warrants was written to prevent exactly this kind of exploratory rummaging through the lives of people who are not suspected of anything. Applying that prohibition to a surveillance economy that has learned to bypass judicial oversight remains an unfinished project. Defense practitioners should be preparing now to challenge not just yesterday’s geofence warrant but tomorrow’s data-broker purchase, tower dump, or reverse-keyword search. The constitutional reckoning with reverse-location surveillance is underway. Chatrie is its beginning, not its conclusion.  

 

Sources: Supreme Court Docket, Chatrie v. United States, No. 25-112 (U.S.); Google LLC, Brief for Amicus Curiae in Support of Neither Party, Chatrie v. United States, No. 25-112 (U.S. Mar. 2, 2026); Petitioner’s Opening Brief, Chatrie v. United States, No. 25-112 (U.S. Feb. 23, 2026); Brief for the United States in Opposition, Chatrie v. United States, No. 25-112 (U.S. Nov. 24, 2025); Brief for the United States, Chatrie v. United States, No. 25-112 (U.S. Mar. 25, 2026); Brief of Amici Curiae American Civil Liberties Union, American Civil Liberties Union of Virginia, Electronic Frontier Foundation, and Center on Privacy & Technology at Georgetown Law in Support of Petitioner, Chatrie v. United States, No. 25-112 (U.S. Mar. 2, 2026); Brief for the Center for Democracy and Technology, Brennan Center for Justice, Surveillance Technology Oversight Project, and Defending Rights & Dissent as Amici Curiae in Support of Petitioner, Chatrie v. United States, No. 25-112 (U.S. Feb. 27, 2026); Brief for the Reporters Committee for Freedom of the Press, Knight First Amendment Institute, and Foundation for Individual Rights and Expression as Amici Curiae in Support of Petitioner, Chatrie v. United States, No. 25-112 (U.S.); Brief for Law & Technology and Fourth Amendment Scholars as Amici Curiae in Support of Petitioner, Chatrie v. United States, No. 25-112 (U.S. Mar. 2, 2026); Brief of Professor Orin S. Kerr as Amicus Curiae in Support of Respondent, Chatrie v. United States, No. 25-112 (U.S. Apr. 1, 2026); Transcript of Oral Argument, Chatrie v. United States, No. 25-112 (U.S. Apr. 27, 2026); Google, Supplemental Information on Geofence Warrants in the United States; Google, Updates to Location History and New Controls Coming Soon to Maps (Dec. 12, 2023); Cong. Rsch. Serv., R48852, Geofence and Keyword Searches: Reverse Warrants and the Fourth Amendment (Feb. 10, 2026); EFF, The Government Uses Targeted Advertising to Track Your Location (Mar. 5, 2026); 404 Media, CBP Tapped Into the Online Advertising Ecosystem To Track People’s Movements (Mar. 3, 2026); Criminal Legal News, Geofence Warrants: The Mass Location Surveillance and Privacy Threat Created by Google May Be Eliminated by Its Creator (Feb. 2024); Criminal Legal News, Fifth Circuit Announces Geofence Warrants Are Unconstitutional Modern-Day General Warrants (Oct. 2024); Meg O’Connor, Avondale Man Sues After Google Data Leads to Wrongful Arrest for Murder, Phoenix New Times (Jan. 16, 2020); Brookings Inst., Supreme Court Agrees to Hear a Fourth Amendment Case Regarding Geofence Warrants (Jan. 27, 2026); Nat’l Ass’n of Crim. Def. Laws., Fourth Amendment Center; Nat’l Ass’n of Crim. Def. Laws., Geofence Warrants; Nat’l Ass’n of Crim. Def. Laws., Reverse Search Warrants; Nat’l Ass’n of Crim. Def. Laws., Geofence Warrant Primer (2022); Nat’l Ass’n of Crim. Def. Laws., Model Motion to Suppress Tower Dump Evidence (Pendergrass); Privacy Impact Assessment for the CBP Commercial Telemetry Data Evaluation, DHS/CBP/PIA-080 (Aug. 12, 2024); Sen. Ron Wyden et al., Letter to Joseph Cuffari, Inspector Gen., Dep’t of Homeland Sec. (Mar. 3, 2026); EFF, Inside Fog Data Science, the Secretive Company Selling Mass Surveillance to Local Police (2022); AP/CBS News, Thanks to Tech, Police Practice “Mass Surveillance on a Budget” (Sept. 1, 2022); Wash. Post, The Powerful Tools in ICE’s Arsenal—And Protesters (Jan. 29, 2026); 404 Media, Inside ICE’s Tool to Monitor Phones in Entire Neighborhoods (Jan. 8, 2026); Lawfare, Data Broker Sales and the Fourth Amendment (Mar. 11, 2024); Criminal Legal News, Federal Government Circumventing Fourth Amendment by Buying Data from Data Brokers (Apr. 15, 2025); Utah Code § 77-23f-102 (2025); H.B. 273, 66th Leg., Gen. Sess. (Utah 2025); S. 404, 2025-2026 Leg., Reg. Sess. (N.Y. 2025); A.B. 793, 2023-2024 Reg. Sess. (Cal. 2023); H.R. 4639, 118th Cong. (2023); EFF, Geofence Warrants and Reverse Keyword Warrants Are So Invasive, Even Big Tech Wants to Ban Them (May 20, 2022); Brennan Ctr. for Just., Closing the Data Broker Loophole; FTC, FTC Reminds Data Brokers of Their Obligations to Comply with PADFAA (Feb. 2026); FedScoop, Privacy Advocates Sound Alarm on “Data Broker Loophole” (Mar. 2026); Lawfare, Limiting Reverse Searches in the Stored Communications Act; ACLU, New Records Detail DHS Purchase and Use of Vast Quantities of Cell Phone Location Data; EPIC, EPIC v. ICE (Location and Social Media Surveillance).

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