Following a car for weeks via a tracking device requires a search warrant , justices say . The justices are divided on what they say makes the action unconstitutional . Justice Alito , for the majority , cites the `` physical intrusion '' of placing the device . " Comment: It's not illegal to use GPS in your vehicle if you're following someone who isn't being followed by police or other law enforcement officers ( e.g. driving down an interstate ) and it
Following a car for weeks via a tracking device requires a search warrant , justices say . The justices are divided on what they say makes the action unconstitutional . Justice Alito , for the majority , cites the `` physical intrusion '' of placing the device . Four others say the lengthy monitoring violated the suspect 's expectation of privacy .