Supreme Court says police can't attach GPS monitors without a warrant.
The Supreme Court has ruled police need a search warrant to track a suspect with GPS.
The justices heard arguments last year in the case of a nightclub owner convicted of drug conspiracy.
Police in Washington, DC had attached a GPS tracking system to his car and followed his movements.
The GPS led investigators to a stash of money and drugs.
Monday's unanimous ruling states they needed a search warrant to put the technology on the car.
A federal appeals court overturned the nightclub owner's conviction.
The decision by the Supreme Court upholds that lower court ruling.