Summary Box: Warrant needed for GPS tracking

THE RULING: The Supreme Court unanimously agreed to bar police from installing GPS technology to track suspects’ movements without first getting a judge’s approval.

DEFEAT FOR LAW ENFORCEMENT: The government and police agencies have been used to getting leeway in investigations following the Sept. 11 attacks. It could complicate law enforcement’s reliance on high tech surveillance of suspects, including the use of various types of GPS technology.

RATIONALE: Justice Antonin Scalia says the government’s installation of a GPS device, and its use to monitor the vehicle’s movements, constitutes a search, meaning that a warrant is required.