Privacy wins GPS test in Supreme Court

The U.S. Supreme Court began the important job of defining the right to privacy in the digital age by ruling yesterday that police violated the Constitution when they attached a global positioning system to a man's car without a valid warrant and tracked his movements for a month.

The court majority said the police ran afoul of the Fourth Amendment's prohibition against unreasonable search and seizure because they physically intruded on the suspect's private property when they planted the device. It's the right call.

Police should be required to convince a judge that there is probable cause to believe a person has committed a crime before allowing his movements to be digitally tracked. It's an important safeguard of individual rights. But the court decided this case on very narrow grounds, leaving for another day, and perhaps a more appropriate set of facts, critical privacy issues linked to digital technology.

In the case before the court, Washington Metropolitan Police, working with an FBI task force, surreptitiously attached the GPS device to the vehicle used by a man they suspected of dealing drugs. The information collected was used to convict him of conspiring to sell cocaine. An appeals court overturned the conviction.

The facts made this case an easy one to decide. But even in the unanimous ruling it's clear the justices are struggling to determine where the legal line should be drawn to protect privacy when technology makes it possible to conduct the surveillance without trespassing on anyone's private property. Would it be permissible, for instance, to use a suspect's smartphone, a factory-installed GPS or other wireless devices to monitor his whereabouts?

Associate Justice Samuel Alito faulted the court's majority for applying 18th century concepts of trespass to 21st century technology. He framed the broader issue that was left unresolved when he said in a concurring opinion that what's important is whether police violated a contemporary, reasonable expectation of privacy.

And what about the different but related legal premise that individuals can have no expectation of privacy regarding information they voluntarily share with third parties? That traditionally has applied to such things as bank records. But, as Associate Justice Sonia Sotomayor suggested in a separate concurring opinion, that premise is ill-suited to the digital age when people reveal so much about themselves -- the phone numbers they dial or text, the address they email, and the books and medications they buy -- to third parties such as cellphone companies, Internet service providers and retailers.

Those key legal issues will have to be resolved. But the court was right to tread slowly.

It didn't have to go beyond the physical trespass involved in attaching the GPS to decide the District of Columbia case. And by basing its ruling on that narrow point, the court has allowed time for a political consensus to develop and, as Alito said may be best, for Congress to fashion a legislative answer to how much privacy the public can realistically expect.