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. Each time a cell phone connects to a cell site, it generates a time-stamped record known as cell-site location information (CSLI). Wireless carriers collect and store CSLI for their own business purposes. Here, after the FBI identified cell phone numbers of several robbery suspects including Carpenter, prosecutors were granted court orders to obtain the suspects’ cell phone records under the Stored Communications Act (SCA). Wireless carriers produced CSLI for Carpenter, including 12,898 location points over 127 days. Carpenter moved to suppress the evidence. The district court denied the motion. Carpenter was convicted of robbery and firearm offenses. He appealed. The Sixth Circuit affirmed, holding Carpenter lacked a reasonable expectation of privacy in the location information because he had shared that information with his wireless carriers, and the resulting business records are not entitled to Fourth Amendment protection. Held: Reversed. The Fourth Amendment protects not only property interests but certain expectations of privacy. An individual has a reasonable expectation of privacy in the whole of his physical movements. Given the pervasive use of modern cell phones, access to CSLI impinges on this expectation by revealing a detailed chronicle of a person’s physical presence compiled every day, every moment, over years. Although a person does not generally have an expectation of privacy in information he shares with third parties, CSLI is unique in its depth, breadth, and deeply revealing nature, as well as the inescapable and automatic nature of its collection. Accordingly, the fact that the cell-site information is held by a third party does not overcome the user’s claim to Fourth Amendment protection. The government’s access to CSLI in this case constituted a search.

The Government must generally obtain a warrant supported by probable cause before acquiring CSLI records; a court order issued under the SCA is not sufficient. A search is generally unreasonable without a warrant supported by probable cause, unless an exception to the warrant requirement applies. Here, the Government acquired the cell-site records pursuant to a court order issued under the SCA, which required the Government to show “reasonable grounds” for believing the records were “relevant and material to an ongoing investigation.” (18 U.S.C. § 2703(d)). Because this showing falls short of the probable cause requirement for a warrant, an order issued under the SCA is not a permissible mechanism for accessing historical cell-site records. Before compelling a wireless carrier to turn over a subscriber’s CSLI, a warrant is required. The court clarified that not all orders compelling the production of documents will require a showing of probable cause, but CSLI is an entirely different species of business record implicating basic Fourth Amendment concerns. While the Government will still be able to use subpoenas to acquire records in the majority of criminal investigations, a warrant is required in the rare case where the suspect has a legitimate privacy interest in the records held by a third party. Furthermore, although the Government will generally need a warrant to access CSLI, case-specific exceptions may support a warrantless search of cell-site records under certain circumstances (e.g. exigent circumstances, including imminent danger or destruction of evidence). [Editor’s Note: Justice Roberts wrote the majority opinion. Justices Kennedy, Thomas, Alito, and Gorsuch each wrote separate dissents.]

The full opinion is available on the court’s website here: https://www.supremecourt.gov/opinions/17pdf/16-402_h315.pdf