The U.S. Supreme Court has ruled that American police must secure a search warrant before they track criminal suspects with the use of global positioning system technology.

The nation's nine-member highest court unanimously decided Monday that law enforcement officials would be violating suspects' constitutional protection against unreasonable searches if they attached a GPS monitoring device to their cars without a court-approved search warrant.

The court made the ruling in a case in which an accused Washington, DC drug dealer was at first convicted, in part on evidence police had accumulated by tracking his movements for 28 days through use of a GPS device. Police spotted the suspect making frequent trips to a house where drugs and $1 million in cash were found. The police had obtained a warrant for use of the GPS device on his car, but the warrant expired before it was installed.

An appellate court had thrown out the suspect's conviction, a ruling the Supreme Court upheld.