The satellite-based Global Positioning Systemis a great way to locate places -- or people.But, last week the United States Supreme Courtruled that law enforcement officials must get approvalfrom a judge before placing a GPS device on a vehicle.The case involved a suspected drug dealer in Washington.Police put a GPS device on his carand tracked his movements for almost a month.That led them to a housewith nearly one hundred kilograms of cocaineand eight hundred fifty thousand dollars in cash.Antoine Jones was found guiltyand sentenced to life in prison.He appealed his case all the way to the Supreme Court.Law professor Christopher Sloboginat Vanderbilt University in Nashville, Tennessee,takes the story from there.CHRISTOPHER SLOBOGIN: "Mr. Jones' arguedthat evidence was obtained illegallybecause the police did not have a warrant.And his argument was in essence that use of the tracking devicewas an unconstitutional search under the Fourth Amendmentto the United States Constitution,which provides that the government may not engagein unreasonable searches and seizures.Mr. Jones claimed that the absence of a warrantmade this search unreasonable."And, says Professor Slobogin, the high court agreed.CHRISTOPHER SLOBOGIN: "All nine members of the court,conservative members as well as liberal members,decided that the Fourth Amendment was violated in this case."But the ruling only dealt with the physical act ofplacing the GPS device on the vehicle and tracking Mr. Jones.Justice Antonin Scalia wrote the majority opinion.Justice Scalia said the case did not require the courtto decide if electronic monitoringwithout trespassing onto someone's propertyis also a violation of privacy.Law professor Renee Hutchins at the University of Marylandsays that is a big question that remains to be answered.We spoke with her on Skype.RENEE HUTCHINS: "Most people have smartphones.A lot of people have cars that have GPS pre-installed.So the government doesn't have to do the installation.The installation, which was the hook for Justice Scalia,is already accomplished. We do it voluntarily."Justice Sonya Sotomayor suggested that modern technologymay soon force us to reconsider expectations of privacy.Professor Hutchins explains.RENEE HUTCHINS: "Justice Sotomayor,actually in talking about the modern society that we live in,said, you know, we really have to perhaps rethinkwhat it means for things to be private in a worldwhere we voluntarily give up so much information.In a world where there's Facebook and GPS on your cell phoneand GPS in your car, how should the court be thinkingabout constitutional protections in a world like that?"Four other justices, led by Samuel Alito,questioned the wisdom of limiting the rulingonly to a trespass of private property.They said the more important issue is the use of GPSfor the purpose of long-term tracking.And that's the VOA Special English Technology Report,written by June Simms.