Carpenter v. United States

Timothy Carpenter was convicted of armed robbery based in part on historical cell-site location information that the FBI obtained from his wireless carrier without a warrant. The data mapped his movements over several days. Carpenter argued that the warrantless acquisition violated his Fourth Amendment right against unreasonable searches. The Supreme Court granted certiorari to decide whether a warrant is required for such records. In a 5-4 decision authored by Chief Justice Roberts, the Court held that accessing cell-site records constitutes a search under the Fourth Amendment. The government’s reliance on the third-party doctrine was rejected in this context because cell phone location data provides an intimate window into a person’s life, revealing associations and patterns. The Court declined to extend the rule that information voluntarily disclosed to third parties enjoys no reasonable expectation of privacy. The case was remanded for further proceedings consistent with the requirement of a warrant.

The Supreme Court held that obtaining historical cell-site records from a wireless carrier is a Fourth Amendment search that generally requires a warrant. The judgment of the Sixth Circuit was reversed and the case was remanded.

Whether the warrantless acquisition of historical cell-site location information from a wireless carrier violates the Fourth Amendment’s prohibition on unreasonable searches, and whether the third-party doctrine eliminates any reasonable expectation of privacy in such digital records.

The ruling reshaped Fourth Amendment jurisprudence for the digital era by significantly limiting the third-party doctrine as applied to sensitive digital data. It established that individuals can retain a reasonable expectation of privacy in location information held by third parties. The decision constrained law enforcement’s ability to conduct warrantless tracking, influenced subsequent lower court decisions on digital searches, and prompted legislative proposals aimed at updating electronic privacy laws. It is widely regarded as a landmark privacy victory.