Blue Brief 2025-2026

Erin Sheley

Professor of Law

Geofence Warrants Trigger the Fourth Amendment After Chatrie v. United States

XI.

T he Supreme Court has set a new guidepost amidst long-evolving doctrinal uncertainty as to how far the Fourth Amendment limits law enforcement’s use of new technologies in investigations. In Chatrie v. United States , the Court held that it constitutes a Fourth Amendment search when police use “geofence” warrants to obtain location data from Google for cell phone users within close physical and temporal proximity to a crime. This result is not terribly surprising in light of the Court’s earlier decision in Carpenter v. United States . However, Chatrie leaves unanswered the arguably more interesting question of whether and under what circumstances such geofence warrants qualify as “reasonable” searches and, thus, pass constitutional muster. The Fourth Amendment protects us from unreasonable searches and seizures, and further provides that police cannot obtain search warrants without “probable cause.” Case law has clarified that — most of the time — a valid

warrant renders a search reasonable, so long as it is based on probable cause that evidence of a crime will be found and describes with particularity the place to be searched or items to be seized. Traditionally, a rule known as the “third-party doctrine” held that information a target voluntarily shares with other people does not implicate the Fourth Amendment, due to the lack of a “ reasonable expectation of privacy ,” and can thus be searched without a warrant. The Court has held that the government could, for example, subpoena financial records from banks or call logs from telephone companies without a warrant based on the idea that the target had implicitly chosen to share this information with the respective providers and given up their reasonable expectation of privacy. Carpenter was previously the most recent in a series of cases in which the Court recognized that the increasingly comprehensive and private nature of the information captured by today’s technology may render the third-party doctrine

UNIVERSITY OF SAN DIEGO SCHOOL OF LAW | Faculty Review of 2025-2026 U.S. Supreme Court Term | Page 35