Carpenter v. United States, 585 U.S. 296, 138 S.Ct. 2206 (2018), is a landmark United States Supreme Court case concerning the privacy of historical cell site location information (CSLI). The Court held that the government violates the Fourth Amendment to the United States Constitution when it accesses historical CSLI records containing the physical locations of cellphones without a search warrant.^[1]

Prior to Carpenter, government entities could obtain cellphone location records from service providers by claiming the information was required as part of an investigation. After Carpenter, government entities are required to obtain a search warrant to access that information. Recognizing the influence of new consumer communications devices in the 2010s, the Court expanded its conceptions of constitutional rights toward the privacy of this type of data. However, the Court emphasized that the Carpenter ruling was narrowly restricted to the precise types of information and search procedures that were relevant to Carpenter's complaint.^[2][3]

Between December 2010 and March 2011, several individuals in the Detroit, Michigan area conspired and participated in armed robberies at RadioShack and T-Mobile stores across the region.^[11] In April 2011, four of the robbers were captured and arrested. The petitioner, Timothy Carpenter, was not among the initial group of arrestees. One of those arrested confessed and turned over his phone so that FBI agents could review the calls made from his phone around the time of the robberies.^[1] The agents obtained a search warrant to inspect the information in that arrestee's phone, in order to find additional contacts of the arrestee and compile more evidence about the crime ring.^[12][13]

From the historical cell site records on the arrestee's phone, the agents confirmed that Timothy Carpenter was also part of the crime ring, and proceeded to compile information about the location of his phone over 127 days. In turn, this information revealed that Carpenter had been within a two-mile radius of four robberies at the times they were perpetrated.^[1] This evidence was used to support Carpenter's arrest. At criminal court, Carpenter was found guilty of several counts of aiding and abetting robberies that affected interstate commerce, and another count of using a firearm during a violent crime. He was sentenced to 116 years in prison.^[14]

Oral arguments

Recording of oral arguments before the Supreme Court.

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Twenty amicus curiae briefs were filed by interested organizations, scholars, and corporations for Carpenter's case.^[19] Some considered the case to be the most important Fourth Amendment dispute to come before the Supreme Court in a generation.^[20][21] The Court issued its decision in 2018, with the majority opinion written by Chief Justice John Roberts.

The Court's ruling recognized that the Carpenter case revealed a contradiction between two lines of Supreme Court rulings on the matter of police searches of personal communications information.^[1] In United States v. Jones (2012) the Court had ruled that GPS tracking could constitute a search under the Fourth Amendment as a violation of a person's reasonable expectation of privacy.^[22] Meanwhile, the Court had held in Smith v. Maryland (1979) that the third-party doctrine absolved the government from warrant requirements when searching through telephone records.^[23]

Ultimately, in Carpenter the court determined that the third-party doctrine could not be extended to historical cell site location information (CSLI). Instead, the Court compared "detailed, encyclopedic, and effortlessly compiled" CSLI records to the GPS information at issue in United States v. Jones, recognizing that both forms of data accord the government the ability to track individuals' past movements.^[24] Furthermore, the Court noted that CSLI could pose even greater privacy risks than GPS data, as the prevalence of cellphones could accord the government "near perfect surveillance" of an individual's movements. Accordingly, the Court ruled that, under the Fourth Amendment, the government must obtain a search warrant in order to access historical CSLI records.^[1]

Roberts argued that technology "has afforded law enforcement a powerful new tool to carry out its important responsibilities. At the same time, this tool risks Government encroachment of the sort the Framers [of the US Constitution], after consulting the lessons of history, drafted the Fourth Amendment to prevent."^[25] As stated in the opinion, "Unlike the nosy neighbor who keeps an eye on comings and goings, they [new technologies] are ever alert, and their memory is nearly infallible. There is a world of difference between the limited types of personal information addressed in Smith [...] and the exhaustive chronicle of location information casually collected by wireless carriers today."^[26]

However, Roberts stressed that the Carpenter decision was a very narrow one and did not affect other parts of the third-party doctrine, such as banking records. Similarly, he noted that the decision did not prevent the collection of CSLI without a warrant in cases of emergency or for issues of national security.^[27]

After the Supreme Court ruling, Carpenter's criminal conviction was remanded to the Sixth Circuit to determine if it could stand without the CSLI data that required a warrant per the Supreme Court. Carpenter's lawyers argued that the data should have been subject to the exclusionary rule and thrown out as material collected without a proper warrant under the Supreme Court's ruling. However, the Circuit Court judges concluded that the FBI was acting in good faith with respect to collecting the data based on the law at the time the crimes were committed.^[33] This type of good faith exemption is permitted per another Supreme Court precedent, Davis v. United States (2011).^[34] The evidence was allowed to stand, and the Sixth Circuit again upheld Carpenter's criminal conviction and prison sentence.^[33]

Meanwhile, the Supreme Court's ruling in Carpenter was very narrow and did not otherwise change the third-party doctrine related to other business records that might incidentally reveal location information, nor did it overrule prior decisions concerning conventional surveillance techniques and tools such as security cameras. The Court did not extend its ruling to other matters related to cellphones not presented in Carpenter, including real-time CSLI or "tower dumps" (the downloading of information about all the devices that were connected to a particular cell site during a particular interval). The opinion also did not consider other data collection goals involving foreign affairs or national security.^[2][3]