The Supreme Court has expressed deep reservations about police use of GPS technology to track criminal suspects without a warrant.

But the justices appeared unsettled Tuesday about how or whether to regulate GPS tracking and other high-tech surveillance techniques.

The court heard arguments in the Obama administration's appeal of a court ruling that threw out a drug conspiracy conviction because FBI agents and local police did not have a valid search warrant when they installed a GPS device on the defendant's car and collected travel information.

The justices were taken aback when the lawyer representing the government said police officers could install GPS devices on the justices' cars and track their movements without a warrant.

The court has previously ruled there is no expectation of privacy on public roads.