Carpenter v. United States

Whether the Fourth Amendment Permits the Government to Obtain Six Months of Cell Phone Location Records Without a Warrant


In Carpenter, the Supreme Court considered the Fourth Amendment standard for the use of mobile location data by law enforcement. The Fourth Amendment guarantees the "right of the people to be secure in their persons, houses, papers, and effects against unreasonable searches and seizures." However, the Supreme Court has not previously had an opportunity to address the application of the Fourth Amendment to many types of modern data, including cell phone location data. Justice Sotomayor famously remarked in her concurring opinion in the 2012 decision in United States v. Jones that it "may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties," an approach that she described as "ill-suited to the digital age." The Court held that mobile location data is protected under the Fourth Amendment, declining to extend the "third-party doctrine" from Smith and Miller to this modern surveillance technique.

In Carpenter v. United States, the Supreme Court reversed the decision of the lower court that seizure and search of 127 days' worth of an individual's cell phone location data was not a "search" under the Fourth Amendment. In the criminal case below, the District Court for the Eastern District of Michigan denied Defendant’s motion to suppress the location data, and later denied post-trial motion for acquittal, and motion for new trial. Carpenter appealed, and the U.S. Court of Appeals for the Sixth Circuit upheld the district court's decision. The government obtained the Defendant's location data under the Stored Communications Act, which requires phone companies to disclose certain historical call records when the government provides “specific and articulable facts showing that there are reasonable grounds to believe” that records at issue “are relevant and material to an ongoing criminal investigation.”

Question Presented

Whether the warrantless seizure and search of historical cell-phone records revealing the location and movements of a cell-phone user over the course of 127 days is permitted by the Fourth Amendment.

Factual Background

This case arises from a criminal investigation in 2010 and 2011. The government obtained more than five months of historical cell phone location records for 16 different phone numbers from various wireless carriers. The magistrates granted the applications pursuant to the Stored Communications Act (“SCA”), which does not require a finding of probable cause. Under the SCA, the government may require the disclosure of telecommunications records when “specific and articulable facts show 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). With the location data provided by the wireless carriers, the agents created maps showing that certain phones had been within a half mile to two miles of certain businesses around the times when robberies had occurred.

The government later charged the defendants with six counts including aiding and abetting robbery that affected interstate commerce—a violation of the Hobbs Act—and aiding and abetting the use or carriage of a firearm during a federal crime of violence.

Technical Background

This case, and other similar cases before federal and state courts, involves the search and seizure of cell phone location data. There are three main types of cell phone location data: (1) historical location data showing prior connections to cell phone towers and/or antennas, (2) real time location data showing current connections to cell phone towers/antennas, and (3) real time location data based on the handset’s GPS signal. Advances in cell phone and cell tower technology have increased the availability and precision of data such that both GPS and tower-based location data can be used to accurately track the location of a cell phone.

Historic Location

The data created when a cell phone communicates with a nearby cell tower can be used to determine the location of any given cell phone and, in turn, its user. Cell phone networks consist of a series of antennas (or “cell sites”). Mobile devices communicate with nearby cell sites during a process called “registration,” which occurs automatically even when the device is idle.1 During the registration process, mobile devices also communicate with nearby cell sites in order to identify the strongest signal. A similar process occurs when a user moves from one cell site to another while making a call. Once registration occurs, the information is stored temporarily in-service provider databases in order to route calls. A log is also typically created every time a call is made or data downloaded, including when smartphone apps access the internet without a user’s knowledge. These logs reveal “which particular cell site a phone was near at the time of the call.” The accuracy of tower-based cell phone location data varies depending on the frequency of connections between the phone and the tower as well as number and proximity of towers. As density increases, so does accuracy. For example, three towers used to triangulate a location can be accurate up to 3/4 of a square mile.

Additionally, data from “small cell” technology, such as microcells and femtocells, can be used to locate a device to within ten feet. The use of this technology in urban environments continues to increase with the number of cell phone users. Municipal governments have partnered with providers to install small cell technology in cities. Verizon is set to place 400 small cells on utility poles in San Francisco and Ericsson installing 100 “Smart Poles” in Los Angeles. There are also indications that machine learning can be applied to historical data to accurately predict not only the home and work of cell phone owners, but potentially the place they are most likely to visit next.

In Carpenter, the Court will consider whether seizure of historical cell phone data obtained from a cell phone provider pursuant to a court order under 18 U.S.C. 2703(d) violates the Fourth Amendment. The data at issue in Carpenter includes logs of which cell towers/antennas were accessed during calls made by the target phones. The court found that “cellphones work by establishing a radio connection with nearby cell towers (or ‘cell sites’); that phones are constantly searching for the strongest signal from those towers; and that individual towers project different signals in each direction or “sector,” so that a cellphone located on the north side of a cell tower will use a different signal than a cellphone located on the south side of the same tower.” The government’s expert had testified that “cell towers are typically spaced widely in rural areas, where a tower’s coverage might reach as far as 20 miles” and that “in an urban area like Detroit, however, each cell site covers ‘typically anywhere from a half-mile to two miles.’” He testified that “wireless carriers typically log and store certain call-detail records of their customers’ calls, including the date, time, and length of each call; the phone numbers engaged on the call; and the cell sites where the call began and ended.”

Real Time Location Data: Cell Towers

Real time or “prospective” cell phone location data from cell towers can be obtained when the provider proactively pings a target phone, rather than waiting for the user to initiate contact with the tower. A request for real time location data may also give the government access to more precise location data generated to comply with the FCC’s E-911 requirements. While this data is created to allow emergency services to locate a cell phone user when they call 911, police and other government officials might request this information in the course of an investigation. Per the FCCs mandate, “[a]ll providers must achieve 50-meter horizontal accuracy or provide dispatchable location for 50 percent of all wireless 911 calls.”

Real Time Location Data: GPS

Several cases have considered the acquisition and use of GPS data during police investigations. GPS receivers in mobile phones can use the satellite signals to calculate “extremely accurate, three-dimensional location information (latitude, longitude and altitude), velocity (speed and direction) and precise time.” However, buildings and other environmental factors in urban areas can reduce the accuracy of GPS location data. GPS data is considered more accurate than cell tower location data and can typically locate a phone within ten meters.

In cases considering the use of GPS data, the police either obtained a warrant or claimed exigent circumstances to justify not obtaining a warrant. United States v. Gilliam, 842 F.3d 801 (2d Cir. 2016) (cert. denied), dealt with cell phone GPS location data obtained without a warrant under 18 U.S.C. 2702(c)(4) due to exigent circumstances. The court held that cell phone location information was included in the statute’s description of “other information” in part by looking at cases interpreting § 2703, and that thus no warrant was needed given the potential danger to a minor. Similarly, in United States v. Caraballo, 831 F.3d 95 (2nd Cir. 2016), officers obtained real time GPS and cell tower location information from Sprint without a warrant due to exigent circumstances.

Procedural History

U.S. District Court for the Eastern District of Michigan

Following their indictment, defendants moved to suppress the introduction of the cell phone location data as evidence, arguing that the data was obtained in violation of the Fourth Amendment and in violation of the standards set forth in the Stored Communications Act, 18 U.S.C. § 2703(d). The trial court denied the motion, rejecting the constitutional argument and holding that the government met the statutory standard. The trial court also denied the defendants’ challenge, on timeliness and reliability grounds, to the testimony of the government’s expert on cell phone data. Defendants were subsequently convicted and filed an appeal to the U.S. Court of Appeals for the Sixth Circuit.

U.S. Court of Appeals for the Sixth Circuit

On appeal, a divided three-judge panel of the Sixth Circuit upheld defendants' convictions. It rejected the argument that the government's efforts to obtain the defendants' location data constituted a “search” under the Fourth Amendment. The court held that the “data themselves took the form of business records created and maintained by Carpenter’s wireless carrier.” When the defendants made or received calls with their cell phones, those phones sent a signal to the nearest cell-tower for the duration of the call. The government thereafter collected those records pursuant to a (non-warrant) court order. The Sixth Circuit found that because the wireless carriers had collected the data “in the ordinary course of business” for their own purposes - including billing matters, to find weak spots in their network and determine whether roaming charges apply - obtaining those records was not a Fourth Amendment search.

The court explained that although the content of personal communications is private, the information necessary to get those communications from point A to point B is not. Because the records simply show which cell towers a phone was connected to at various times, without providing any information about the content of the calls, the cell phone user has no expectations of privacy in the location data. The court relied on a finding that the defendants had voluntarily revealed their location data to the phone company and that subsequent seizure of that data was not a search under United States v. Miller, 425 U.S. 435, 443, (1976), and Smith v. Maryland, 442 U.S. 735 (1979).

Concurring in the judgment only, Judge Stranch explained that “the sheer quantity of sensitive information procured without a warrant in this case raises Fourth Amendment concerns of the type the Supreme Court acknowledged in United States v. Jones, 132 S. Ct. 945, 964 (2012) (Alito, j., concurring).” The court denied re hearing en banc on June 29, 2016.

On September 26, 2016, Carpenter filed a petition for a writ of certiorari, which the Supreme Court granted on June 5, 2017. The case will be heard in Fall 2017.

EPIC's Interest

EPIC has an interest in promoting privacy in digital spaces by upholding robust Fourth Amendment protections, including for data stored remotely by service providers. Location privacy is an increasingly important issue as more devices generate and store data that can be used to track individuals' movements over time, revealing the most intimate and private details of their lives and also chilling their First Amendment protected activities.

EPIC has filed many amicus curiae briefs in Supreme Court, Federal Court, and State cases related to location tracking and seizure of private communications records. See for example, EPIC: United States v. Jones; EPIC: In re US Application for Historic Cell-Site Location Information; EPIC: State v. Earls. The case concerns a critical question that will shape the application of the Fourth Amendment to digital data -- whether the Government must obtain a warrant before forcing a company to disclose private customer records. EPIC has argued that cell phone location records reveal sensitive information and should be protected even if that data is held by wireless carriers. For more information, see EPIC: Location Privacy.

EPIC also highlighted the dangers of location-tracking technology in People, Not Places, A Policy Framework for Analyzing Location Privacy Issues. EPIC closely monitors and provides information about privacy-invasive technologies. In this context, EPIC previously sued the FBI for details ont he use of "Sting Ray" cell phone tracking devices. EPIC's suit against the FBI revealed details of the Government's use of a cell phone tracking technology, known as a StingRay. For more than 15 years the FBI has used this "cell-site simulator" technology to track the location of cell phones and other communications devices. Cell-site simulators act like a fake cell towers and can be used to monitor and track cell phone users even when the device is not in use. The technique also tracks all individuals in a region, regardless of whether they are the suspect in an investigation.

Legal Documents

United States Supreme Court, No. 16-402

Merits Stage

Petition Stage

U.S. Court of Appeals for the Sixth Circuit, Nos. 14-1572/1805

U.S. District Court for the Eastern District of Michigan, No. 12-20218


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