SCOTUS has ruled, sticking a GPS transponder on a car without a warrant is bad. It was unanimous. The details of the case concerned a drug dealer, and the attempt by law enforcement to monitor the car for 28 days. Interesting though that the rationale for the option was divided 5-4 with Scalia writing for the majority and Roberts Jr. Kennedy, Thomas and Sotomayor joining in on the majority opinion. They wrote, "We hold that the government’s installation of a G.P.S. device on a target’s vehicle, and its use of that device to monitor the vehicle’s movements, constitutes a search."
So far so good. But the 4 concurring justices pointed out that the majority just used 18th-century legal concepts on a 21st-century technology. They were looking for a contemporary argument on a reasonable expectation of privacy. Alito, Ginsburg, Breyer and Kagan joined the concurrence.