On June 22, 2018, the United States Supreme Court decided Carpenter v. U.S., No. 16-402, holding that law enforcement, absent exigent circumstances, must get a warrant to obtain cell-site location information (CSLI) that extends over a period of time.

After a series of robberies around Detroit, police arrested four men. One of the men identified possible additional accomplices and cell phone numbers. With that information, prosecutors applied and were granted court orders under the Stored Communications Act, 18 U.S.C. § 2703(d) for CSLI for Carpenter’s telephone. One carrier produced 127 days of information and another two days of information, which provided 12,898 location points for Carpenter during that time. Carpenter moved to suppress the CSLI, arguing the government’s seizure of the information violated the Fourth Amendment because it was obtained without a warrant supported by probable cause. The district court denied the motion, and Carpenter was convicted. The Sixth Circuit affirmed.

The Supreme Court reversed and remanded, holding that to obtain CSLI that details a person’s movements over a period of time, law enforcement must obtain a warrant supported by probable cause. The Court reasoned first that although a person generally does not have a reasonable expectation of privacy in his or her public movements, CSLI information “provides an all-encompassing record” of a person’s whereabouts. As a result, not only are movements revealed, but also matters like family, political, and professional associations, in which a person does have a reasonable expectation of privacy. CSLI provides law enforcement information that is otherwise unknowable, limited only by phone carriers’ retention policies.

The Court also reasoned that CSLI is not accessible under the third-party doctrine, which provides that a person has a reduced expectation of privacy in information he or she knowingly shares with another. The Court noted that short of disconnecting a phone from a network, there is no way to avoid sharing location information with a cell phone carrier. Thus, the fact the information was obtained from a third party does not take the search outside the Fourth Amendment.

The Court noted its decision is narrowly focused on historical CSLI and does not eliminate the government’s ability to obtain the information without a warrant in the face of exigent circumstances, such as bomb threats, active shootings, and child abductions.

Chief Justice Roberts delivered the opinion of the Court, in which Justices Ginsburg, Breyer, Sotomayor, and Kagan joined. Justice Kennedy filed a dissenting opinion, in which Justices Thomas and Alito joined. Justice Thomas filed a dissenting opinion. Justice Alito filed a dissenting opinion, in which Justice Thomas joined. Justice Gorsuch filed a dissenting opinion.

Download Opinion of the Court.