The Supreme Court of the United States unanimously ruled on Monday that police must obtain a warrant before placing a GPS tracking device on the vehicle of a suspect. The decision is considered the first major decision to clarify constitutional privacy rights in the digital age.

The ruling upheld the decision of an appeals court which overturned the conviction of a nightclub owner charged with drug possession. Police obtained that conviction with evidence gathered by means of a GPS tracking device which was placed on the man's car.

At the time the device was placed on the man's vehicle, police did not have a valid search warrant. They had apparently obtained a warrant in Maryland, but the device was not attached to the man's car until it had moved to Washington D.C., and by that time the warrant was expired anyway. They never attempted, apparently, to get a valid license for the District of Columbia.

Justice Scalia, writing for the court, said that the Fourth Amendment protection against unreasonable searches and seizures extends to personal property, including a person's vehicle. Using the device to monitor a vehicle's movements is a "search" and a warrant is required.

Justice Alito wrote a concurring opinion noting that the search violated Fourth Amendment protection precisely because it violated the suspect's reasonable expectation of privacy.

The government argued in the case that the government's surveillance of the man through a tracking device was reasonable since there is no expectation of privacy for a vehicle on public roads.

One of the issues that the question did not address was at what point the long-term surveillance of the vehicle became a search within the meaning of the constitution. That question and others will surely have to be hashed out in other similar cases, which are sure to come.

Source: Fox News, "Supreme Court: GPS devices equivalent to search, police must get warrant," January 23, 2012.