Dunn v. United States of America

On November 7, 2025, Marcus Dunn, a cybersecurity researcher, discovered that the FBI had been collecting his real-time geolocation data without a warrant for over a year under a classified national security program. The data was obtained from his mobile carrier through an administrative subpoena, not a judicial warrant. Dunn filed a federal lawsuit alleging a violation of his Fourth Amendment rights against unreasonable searches. The case reached the U.S. Supreme Court after lower courts split on whether the third-party doctrine applied. Dunn argued that continuous, long-term location tracking reveals intimate details of a person’s life, requiring a warrant. The government contended that the data was a business record voluntarily shared with the carrier. The Court heard arguments on the retroactive application of its 2018 Carpenter decision to real-time tracking and the scope of the third-party doctrine in the context of persistent surveillance.

The Supreme Court ruled 6-3 in favor of Dunn, holding that prolonged, warrantless collection of real-time location data violates the Fourth Amendment. The decision extended Carpenter v. United States, establishing that individuals retain a reasonable expectation of privacy in the whole of their physical movements, even when data is held by a third party. The program was required to cease pending warrant-based procedures.

Whether the warrantless acquisition of a citizen’s real-time geolocation data from a third-party carrier over an extended period constitutes a search under the Fourth Amendment, thereby requiring a judicial warrant.

The ruling significantly curtailed government surveillance powers, establishing a clear warrant requirement for real-time digital tracking. It prompted legislative proposals to update electronic privacy laws, sparked public debate on the balance between national security and civil liberties, and forced technology and telecom companies to revise data-sharing policies with law enforcement.