The US Supreme Court ruled on Monday that police need a search warrant before tracking a suspect with a GPS device, in a case involving privacy and 21st century technology.

The highest US court ruled 9-0 that police had violated the rights of a suspected drug dealer when they placed a GPS, or Global Positioning System, tracking device, on his vehicle without a warrant and tracked his movements.

The Fourth Amendment of the US Constitution provides guarantees against unreasonable search and seizure.

"We hold that the government's installation of a GPS device on a target's vehicle, and its use of that device to monitor the vehicle's movements, constitutes a 'search,'" Justice Antonin Scalia wrote.

"The government physically occupied private property for the purpose of obtaining information," Scalia said. "By attaching the device to the Jeep, officers encroached on a protected area."

The case stems from the conviction of Antoine Jones, a Washington DC nightclub owner who was suspected of drug dealing.

Police had obtained a warrant to place a GPS device on Jones's car but they did not remove it when the warrant expired. They reinstalled the device and subsequently tracked Jones's movements for 28 days.

Police used the GPS device to track Jones to a stash house, where they found cocaine, weapons and drug paraphernalia. He was convicted of conspiracy to distribute cocaine and sentenced to life in prison.

His conviction was overturned by the Court of Appeals for the DC Circuit and Monday's Supreme Court ruling upholds the decision of the lower court.

The case was seen as an important test of how far police can go in using technology to investigate and track suspects.

It drew wide interest from civil liberties groups amid concern that new technologies can be used to get around constitutional protections of privacy and other rights.

During oral arguments in November, Justice Stephen Breyer said to government attorneys, "If you win this case, there is nothing preventing you from monitoring the movements of every citizen of the United States 24 hours a day.

"If you win, you produce something that sounds like '1984,'" Breyer said, making a reference to the George Orwell novel.

The Washington-based Center for Democracy and Technology (CDT) described the ruling as a "landmark decision."

"The Supreme Court today made it clear that it will not allow advancing technology to erode the constitutional right of privacy," said Gregory Nojeim, director of the CDT's Project on Freedom, Security and Technology.

The CDT said the case also has implications for the use of cellphone tower data to track individuals.

"Cell phone triangulation can be just as precise as GPS," Nojeim said.

"Congress should build on this opinion by writing a statute that draws a bright line requiring the government, except in emergencies, to get a warrant before turning your cellphone into a tracking device," he said. (AFP)