In US vs. Jones, the US Supreme Court was asked to decide whether the attachment of a Global Positioning-System (GPS) tracking device to an individual's vehicle, and subsequent use of that device to monitor the vehicle's movements on public streets, constitutes a search or seizure within the meaning of the Fourth Amendment.
The Fourth Amendment provides in relevant part that "[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated."
In a unanimous decision, the Supreme Court ruled that police cannot attach a GPS device to a criminal suspect's car to track their movements without first obtaining a search warrant.
While the Government contended that no "search" occurred, the Court thought differently. It is beyond dispute that a vehicle is an "effect" as that term is used in the Amendment. United States v. Chadwick, 433 U. S. 1, 12 (1977). Based on this, the Court reasoned that the Government's installation of a GPS device on a target's vehicle, and its use of that device to monitor the vehicle's movements, constitutes a "search."
Associate Justice Antonin Scalia said that the government's installation of a GPS device, and its use to monitor a vehicle's movements, constitutes a search, meaning that a warrant is required.
"By attaching the device to the Jeep" that Jones was using, "officers encroached on a protected area," Scalia wrote.
This is probably not the end of these types of cases making their way to the US Supreme Court because the court did not rule on whether the exact search was reasonable, which means even if the Fourth Amendment applies in cases like this, it's possible that the use of GPS devices may be considered acceptable in some circumstances.