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Carpenter Slowly Remaking Fourth Amendment Case Law

The U.S. Supreme Court issued a landmark decision in 2018, which has been slowly changing the way courts interpret the Fourth Amendment of the U.S. Constitution in our era of mobile technology — and impacting the day-to-day investigative efforts of police.

In Carpenter v. United States, 138 S. Ct. 2206 (2018), the Supreme Court ruled that the Fourth Amendment protects data generated by mobile phones known as historical cell-site location information. Previously, police departments could make informal requests of telecom companies to produce this data.

The Court said such information creates a “detailed chronicle of a person’s physical presence compiled every day, every moment over years” and that police must obtain a warrant before accessing this data.

Since the Court issued its decision in Carpenter, it has been cited in over 450 criminal and civil cases across the country.

Lower courts are applying Carpenter in ways that limit the investigative techniques of police because the nation’s top court has signaled this shift in how we should view the expectation of privacy in a world where technology facilitates sharing personal details with third parties (usually large corporations).

In Commonwealth v. Almonor, 120 N.E.3d 1183 (Mass. 2019), and State v. Muhammad, 451 P.3d 1060 (Wash. 2019), the courts applied Carpenter to require a search warrant before police may “ping” a cellphone to obtain its present location or the location of the vehicle.

In United States v. Moore-Bush, 381 F. Supp. 3d 139 (D. Mass. 2019), and People v. Tafoya, 2019 Colo. App. LEXIS 1799 (2019), the courts ruled the use of digital cameras mounted on poles, which can watch a person’s home or backyard for months on end, also violate our expectation of privacy and “provokes an immediate negative visceral reaction,” raising “the specter of the Orwellian state.” Just because a space is visible by the public does not mean police can observe and record it for months.

Databases of otherwise innocuous information also can be problematic. Police have been collecting data from automated license plate readers and use this data to create an aggregate portrait of a person’s life, including sensitive data like travel to doctor offices and places of worship.

Android and iPhone user-location data are also collected over time, and police have used “geofence warrants” to determine who was nearby when a crime was committed, an attempt to backtrack criminals, but which also sweeps up hundreds of innocent citizens for close scrutiny.

Police have used genetic databases in around 200 cases in 2019. Research shows that 60 percent of white Americans could be easily identified by using one database alone.

These tactics amount to the kind of “fishing expeditions” the Fourth Amendment drafters intended to protect us against.

Carpenter will continue to shape the intersection of technology and the law and will hopefully continue to curtail some of the most egregious abuses of modern surveillance by authorities. 


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Related legal case

Carpenter v. U.S.

Supreme Court of the United States
885 U.S. ___; 138 S.Ct. ___; 200 L.Ed.2d ___; 2018 U.S. LEXIS 3844 *


November 29, 2017, Argued;
June 22, 2018, Decided

No. 16-402.

Notice: The LEXIS pagination of this document is subject to change pending release of the final published version.

United States v. Carpenter, 819 F.3d 880, 2016 U.S. App. LEXIS 6670 (6th Cir.), 2016 FED App. 89P (6th Cir.) (6th Cir. Mich., Apr. 13, 2016)

Disposition: Reversed and remanded.


Cell phones perform their wide and growing variety of functions by continuously connecting to a set of radio antennas called “cell sites.” Each time a phone connects to a cell site, it generates a time-stamped record known as cell-site location information (CSLI). Wireless carriers collect and store this information for their own business purposes. Here, after the FBI identified the cell phone numbers of several robbery suspects, prosecutors were granted court orders to obtain the suspects’ cell phone records under the Stored Communications Act. Wireless carriers produced CSLI for petitioner Timothy Carpenter’s phone, and the Government was able to obtain 12,898 location points cataloging Carpenter’s movements over 127 days—an average of 101 data points per day. Carpenter moved to suppress the data, arguing that the Government’s seizure of the records without obtaining a warrant supported by probable cause violated the Fourth Amendment. The District Court denied the motion, and prosecutors used the records at trial to show that Carpenter’s phone was near four of the robbery locations at the time [*2] those robberies occurred. Carpenter was convicted. The Sixth Circuit affirmed, holding that Carpenter lacked a reasonable expectation of privacy in the location information collected by the FBI because he had shared that information with his wireless carriers.


1. The Government’s acquisition of Carpenter’s cell-site records was a Fourth Amendment search. Pp. 4-18.

(a) The Fourth Amendment protects not only property interests but certain expectations of privacy as well. Katz v. United States, 389 U. S. 347, 351, 88 S. Ct. 507, 19 L. Ed. 2d 576. Thus, when an individual “seeks to preserve something as private,” and his expectation of privacy is “one that society is prepared to recognize as reasonable,” official intrusion into that sphere generally qualifies as a search and requires a warrant supported by probable cause. Smith v. Maryland, 442 U. S. 735, 740, 99 S. Ct. 2577, 61 L. Ed. 2d 220 (internal quotation marks and alterations omitted). The analysis regarding which expectations of privacy are entitled to protection is informed by historical understandings “of what was deemed an unreasonable search and seizure when [the Fourth Amendment] was adopted.” Carroll v. United States, 267 U. S. 132, 149, 45 S. Ct. 280, 69 L. Ed. 543, T.D. 3686. These Founding-era understandings continue to inform this Court when applying the Fourth Amendment to innovations in surveillance tools. See, e.g., Kyllo v. United States, 533 U. S. 27, 121 S. Ct. 2038, 150 L. Ed. 2d 94. Pp. 4-7.

(b) The digital data at issue—personal location information maintained by [*3] a third party—does not fit neatly under existing precedents but lies at the intersection of two lines of cases. One set addresses a person’s expectation of privacy in his physical location and movements. See, e.g., United States v. Jones, 565 U. S. 400, 132 S. Ct. 945, 181 L. Ed. 2d 911 (five Justices concluding that privacy concerns would be raised by GPS tracking). The other addresses a person’s expectation of privacy in information voluntarily turned over to third parties. See United States v. Miller, 425 U. S. 435, 96 S. Ct. 1619, 48 L. Ed. 2d 71 (no expectation of privacy in financial records held by a bank), and Smith, 442 U. S. 735, 99 S. Ct. 2577, 61 L. Ed. 2d 220 (no expectation of privacy in records of dialed telephone numbers conveyed to telephone company). Pp. 7-10.

(c) Tracking a person’s past movements through CSLI partakes of many of the qualities of GPS monitoring considered in Jones—it is detailed, encyclopedic, and effortlessly compiled. At the same time, however, the fact that the individual continuously reveals his location to his wireless carrier implicates the third-party principle of Smith and Miller. Given the unique nature of cell-site records, this Court declines to extend Smith and Miller to cover them. Pp. 10-18.

(1) A majority of the Court has already recognized that individuals have a reasonable expectation of privacy in the whole of their physical [*4] movements. Allowing government access to cell-site records—which “hold for many Americans the ‘privacies of life,’” Riley v. California, 573 U. S. ___, ___-___, 134 S. Ct. 2473, 189 L. Ed. 2d 430 contravenes that expectation. In fact, historical cell-site records present even greater privacy concerns than the GPS monitoring considered in Jones: They give the Government near perfect surveillance and allow it to travel back in time to retrace a person’s whereabouts, subject only to the five-year retention policies of most wireless carriers. The Government contends that CSLI data is less precise than GPS information, but it thought the data accurate enough here to highlight it during closing argument in Carpenter’s trial. At any rate, the rule the Court adopts “must take account of more sophisticated systems that are already in use or in development,” Kyllo, 533 U. S., at 36, 121 S. Ct. 2038, 150 L. Ed. 2d 94, and the accuracy of CSLI is rapidly approaching GPS-level precision. Pp. 12-15.

(2) The Government contends that the third-party doctrine governs this case, because cell-site records, like the records in Smith and Miller, are “business records,” created and maintained by wireless carriers. But there is a world of difference between the limited types of personal information addressed in Smith and Miller and the exhaustive [*5] chronicle of location information casually collected by wireless carriers.

The third-party doctrine partly stems from the notion that an individual has a reduced expectation of privacy in information knowingly shared with another. Smith and Miller, however, did not rely solely on the act of sharing. They also considered “the nature of the particular documents sought” and limitations on any “legitimate ‘expectation of privacy’ concerning their contents.” Miller, 425 U. S., at 442, 96 S. Ct. 1619, 48 L. Ed. 2d 71. In mechanically applying the third-party doctrine to this case the Government fails to appreciate the lack of comparable limitations on the revealing nature of CSLI.

Nor does the second rationale for the third-party doctrine—voluntary exposure—hold up when it comes to CSLI. Cell phone location information is not truly “shared” as the term is normally understood. First, cell phones and the services they provide are “such a pervasive and insistent part of daily life” that carrying one is indispensable to participation in modern society. Riley, 573 U. S., at ___, 134 S. Ct. 2473, 189 L. Ed. 2d 430. Second, a cell phone logs a cell-site record by dint of its operation, without any affirmative act on the user’s part beyond powering up. Pp. 15-17.

(d) This decision is narrow. It does not express a [*6] view on matters not before the Court; does not disturb the application of Smith and Miller or call into question conventional surveillance techniques and tools, such as security cameras; does not address other business records that might incidentally reveal location information; and does not consider other collection techniques involving foreign affairs or national security. Pp. 17-18.

2. The Government did not obtain a warrant supported by probable cause before acquiring Carpenter’s cell-site records. It acquired those records pursuant to a court order under the Stored Communications Act, which required the Government to show “reasonable grounds” for believing that the records were “relevant and material to an ongoing investigation.” 18 U. S. C. §2703(d). That showing falls well short of the probable cause required for a warrant. Consequently, an order issued under §2703(d) is not a permissible mechanism for accessing historical cell-site records. Not all orders compelling the production of documents will require a showing of probable cause. A warrant is required only in the rare case where the suspect has a legitimate privacy interest in records held by a third party. And even though the Government will generally [*7] need a warrant to access CSLI, case-specific exceptions—e.g., exigent circumstances—may support a warrantless search. Pp. 18-22.

819 F. 3d 880, reversed and remanded.

Counsel: Nathan F. Wessler argued the cause for petitioner.

Michael R. Dreeben argued the cause for respondent.

Judges: Roberts, C. J., delivered the opinion of the Court, in which Ginsburg, Breyer, Sotomayor, and Kagan, JJ., joined. Kennedy, J., filed a dissenting opinion, in which Thomas and Alito, JJ., joined. Thomas, J., filed a dissenting opinion. Alito, J., filed a dissenting opinion, in which Thomas, J., joined. Gorsuch, J., filed a dissenting opinion.

Opinion by: ROBERTS

Chief Justice Roberts delivered the opinion of the Court.

This case presents the question whether the Government conducts a search under the Fourth Amendment when it accesses historical cell phone records that provide a comprehensive chronicle of the user’s past movements.


There are 396 million cell phone service accounts in the United States—for a Nation of 326 million people. Cell phones perform their wide and growing variety of functions by connecting to a set of radio antennas called “cell sites.” Although cell sites are usually mounted on a tower, they can also be found on light posts, flagpoles, church steeples, or the sides of buildings. Cell sites typically have several directional antennas that divide [*8] the covered area into sectors.

Cell phones continuously scan their environment looking for the best signal, which generally comes from the closest cell site. Most modern devices, such as smartphones, tap into the wireless network several times a minute whenever their signal is on, even if the owner is not using one of the phone’s features. Each time the phone connects to a cell site, it generates a time-stamped record known as cell-site location information (CSLI). The precision of this information depends on the size of the geographic area covered by the cell site. The greater the concentration of cell sites, the smaller the coverage area. As data usage from cell phones has increased, wireless carriers have installed more cell sites to handle the traffic. That has led to increasingly compact coverage areas, especially in urban areas.

Wireless carriers collect and store CSLI for their own business purposes, including finding weak spots in their network and applying “roaming” charges when another carrier routes data through their cell sites. In addition, wireless carriers often sell aggregated location records to data brokers, without individual identifying information of the sort at [*9] issue here. While carriers have long retained CSLI for the start and end of incoming calls, in recent years phone companies have also collected location information from the transmission of text messages and routine data connections. Accordingly, modern cell phones generate increasingly vast amounts of increasingly precise CSLI.

In 2011, police officers arrested four men suspected of robbing a series of Radio Shack and (ironically enough) T-Mobile stores in Detroit. One of the men confessed that, over the previous four months, the group (along with a rotating cast of getaway drivers and lookouts) had robbed nine different stores in Michigan and Ohio. The suspect identified 15 accomplices who had participated in the heists and gave the FBI some of their cell phone numbers; the FBI then reviewed his call records to identify additional numbers that he had called around the time of the robberies.

Based on that information, the prosecutors applied for court orders under the Stored Communications Act to obtain cell phone records for petitioner Timothy Carpenter and several other suspects. That statute, as amended in 1994, permits the Government to compel the disclosure of certain telecommunications [*10] records when it “offers specific and articulable facts showing that there are reasonable grounds to believe” that the records sought “are relevant and material to an ongoing criminal investigation.” 18 U. S. C. §2703(d). Federal Magistrate Judges issued two orders directing Carpenter’s wireless carriers—MetroPCS and Sprint—to disclose “cell/site sector [information] for [Carpenter’s] telephone[ ] at call origination and at call termination for incoming and outgoing calls” during the four-month period when the string of robberies occurred. App. to Pet. for Cert. 60a, 72a. The first order sought 152 days of cell-site records from MetroPCS, which produced records spanning 127 days. The second order requested seven days of CSLI from Sprint, which produced two days of records covering the period when Carpenter’s phone was “roaming” in northeastern Ohio. Altogether the Government obtained 12,898 location points cataloging Carpenter’s movements—an average of 101 data points per day.

Carpenter was charged with six counts of robbery and an additional six counts of carrying a firearm during a federal crime of violence. See 18 U. S. C. §§924(c), 1951(a). Prior to trial, Carpenter moved to suppress the cell-site data provided by the wireless [*11] carriers. He argued that the Government’s seizure of the records violated the Fourth Amendment because they had been obtained without a warrant supported by probable cause. The District Court denied the motion. App. to Pet. for Cert. 38a-39a.

At trial, seven of Carpenter’s confederates pegged him as the leader of the operation. In addition, FBI agent Christopher Hess offered expert testimony about the cell-site data. Hess explained that each time a cell phone taps into the wireless network, the carrier logs a time-stamped record of the cell site and particular sector that were used. With this information, Hess produced maps that placed Carpenter’s phone near four of the charged robberies. In the Government’s view, the location records clinched the case: They confirmed that Carpenter was “right where the . . . robbery was at the exact time of the robbery.” App. 131 (closing argument). Carpenter was convicted on all but one of the firearm counts and sentenced to more than 100 years in prison.

The Court of Appeals for the Sixth Circuit affirmed. 819 F. 3d 880 (2016). The court held that Carpenter lacked a reasonable expectation of privacy in the location information collected by the FBI because he had shared that information [*12] with his wireless carriers. Given that cell phone users voluntarily convey cell-site data to their carriers as “a means of establishing communication,” the court concluded that the resulting business records are not entitled to Fourth Amendment protection. Id., at 888 (quoting Smith v. Maryland, 442 U. S. 735, 741, 99 S. Ct. 2577, 61 L. Ed. 2d 220 (1979)).

We granted certiorari. 582 U. S. ___, 137 S. Ct. 2211, 198 L. Ed. 2d 657 (2017).


HN1 The Fourth Amendment protects “[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.” The “basic purpose of this Amendment,” our cases have recognized, “is to safeguard the privacy and security of individuals against arbitrary invasions by governmental officials.” Camara v. Municipal Court of City and County of San Francisco, 387 U. S. 523, 528, 87 S. Ct. 1727, 18 L. Ed. 2d 930 (1967). The Founding generation crafted the Fourth Amendment as a “response to the reviled ‘general warrants’ and ‘writs of assistance’ of the colonial era, which allowed Brit



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