Carpenter v. United States

Federal investigators obtained Timothy Carpenter's historical cell-site location information from wireless carriers using Stored Communications Act court orders, not a probable-cause warrant. The records included 12,898 location points over 127 days and helped place his phone near robbery locations.

Carpenter moved to suppress the data after conviction.

The dispute reached the courts because the police action, prosecution, civil-rights claim, or government policy raised a constitutional question that could not be answered by the facts alone.

Does the government's acquisition of historical cell-site location information from a wireless carrier constitute a Fourth Amendment search requiring a warrant supported by probable cause?

In plain English, the court had to decide where police authority ended and constitutional protection began under the facts of this case.

Yes. The Supreme Court held that acquiring Carpenter's historical cell-site records was a Fourth Amendment search. In general, police must get a warrant supported by probable cause before obtaining such extensive CSLI, though the Court left room for exceptions like exigent circumstances.

The decision matters because carpenter limits the third-party doctrine for modern digital location data. Even though wireless carriers hold the records, long-term cell-site data can reveal a detailed chronicle of a person's movements and therefore receives Fourth Amendment protection.

Police usually need a warrant before getting a person's long-term cell phone location history from a carrier.

Carpenter remains a central digital privacy case for law enforcement requests involving historical location records, geofence data, app location histories, and other surveillance tools that can reconstruct a person's movements over time.