WASHINGTON, District of Colombia - The US Supreme Court has ruled unanimously that police must get a search warrant before using GPS technology to track cars used by criminal suspects.The decision was a defeat for the government and police agencies and raises the possibility of serious complications for law enforcement nationwide, which increasingly relies on high-tech surveillance of suspects - including the use of various types of GPS technology.WARRANT REQUIREDA GPS device installed by police on Washington night-club owner Antoine Jones' Jeep helped them link him to a suburban house used to stash money and drugs. He was sentenced to life in prison before the Appeals Court overturned the conviction.Associate Justice Antonin Scalia said the government's installation of a GPS device, and its use to monitor the vehicle's movements, constituted a search, meaning a warrant was required."By attaching the device to the Jeep officers encroached on a protected area," Scalia wrote. He concluded that the installation of the device on the vehicle without a warrant was a trespass and therefore an illegal search.All nine justices agreed that the GPS monitoring on the Jeep violated protections in the Fourth Amendment of the US Constitution against unreasonable search and seizure, a decision the American Civil Liberties Union said was “an important victory for privacy”.DIFFERENT REASONSWashington lawyer Andy Pincus called the decision "a landmark ruling in applying the Fourth Amendment's protections to advances in surveillance technology”. Pincus has argued 22 cases before the Supreme Court and filed a brief in the current case on behalf of the Centre for Democracy and Technology, a civil liberties group with expertise in law, technology, and policy.Scalia wrote the main opinion of three in the case. He was joined by Chief Justice John Roberts and justices Anthony Kennedy, Clarence Thomas and Sonia Sotomayor.Sotomayor also wrote one of the two concurring opinions that agreed with the outcome in the Jones case for different reasons.Justice Samuel Alito wrote, in the other concurring opinion, that the trespass was not as important as the suspect's expectation of privacy. Police monitored the Jeep's movements over the course of four weeks after attaching the GPS device.PRECISION NOT NEEDED"The use of longer-term GPS monitoring in investigations of most offences impinges on expectations of privacy," Alito wrote in an opinion joined by justices Ruth Bader Ginsburg, Stephen Breyer and Elena Kagan. Sotomayor, in her concurring opinion, specifically said she agreed with Alito on this conclusion.Alito added: "We need not identify with precision the point at which the tracking of this vehicle became a search, for the line was surely crossed before the four-week mark."Regarding the issue of duration, Scalia wrote that "we may have to grapple" with those issues in the future, "but there is no reason for rushing forward to resolve them here”.Alito also said the court should address how expectations of privacy affected whether warrants were required for remote surveillance using electronic methods that do not require the police to install equipment, such as GPS tracking of mobile telephones.FRIENDLY TRACKING OK Alito noted, for example, that more than 322-million cellphones have installed equipment that allows wireless carriers to track the phone's location."If long-term monitoring can be accomplished without committing a technical trespass - suppose for example, that the federal government required or persuaded auto manufacturers to include a GPS tracking device in every car - the court's theory would provide no protection.”Sotomayor agreed. "It may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to other parties.”A federal appeals court in Washington had overturned Jones's drug conspiracy conviction because police did not have a warrant when they installed a GPS device on his vehicle and then tracked his movements for a month.The Supreme Court agreed with the appeals court. (The case is US v. Jones, 10-1259).