The Supreme Court has heard arguments in a case that asks what role the Fourth Amendment will play in the 21st century, when satellite systems, GPS devices and smartphones increasingly make it possible for the government to track our every move without human intervention.

At stake is whether technology has overtaken privacy and whether the Constitution has anything to say about it.

If we are to retain the privacy essential to a free society that the Framers sought to protect, technology must be regulated by the amendment that prohibits unreasonable searches and seizures.

But to do so, the Supreme Court may need to revise its interpretation of the Fourth Amendment.

The court has been here before. In 1967, it belatedly ushered the Fourth Amendment into the 20th century when it ruled in Katz v. United States that before the government wiretaps a citizen’s phone, it must get a warrant based on probable cause.

The court had previously ruled that the police needed a warrant only when their search actually invaded property.

Since wiretaps could be installed far from a suspect’s property, the court had deemed them to be of no constitutional concern.

In Katz, however, the court recognized that unless the rules were changed, privacy would be rendered obsolete by technological advances. Proclaiming that the Fourth Amendment “protects people, not places,” it ruled that, whenever the government invades a “reasonable expectation of privacy,” it must satisfy the Fourth Amendment and that people reasonably expect their phone calls to be private.

The court may now need to update constitutional doctrine again to account for more recent technological innovations.

In the case heard on Nov. 15, United States v. Jones, the police secretly attached a global positioning device to the underside of a suspect’s car, turning the car into a 24-7 surveillance tool that tracked his every move and, after a month, led them to a large cache of cocaine.

The government did not have a valid warrant, but the Justice Department argued that it didn’t need one. Because the police used the GPS device to gather evidence of the car’s location only on public roads, the administration said, police invaded no privacy and required no warrant.

If the court were to accept this reasoning, nothing in the Constitution would stop the government from using GPS devices to track all of us, all of the time, without our consent or basis for suspicion.

Or as Chief Justice John Roberts noted during oral argument, bringing the matter even closer to home, nothing would stop the FBI from placing GPS equipment on each of the justices’ cars and monitoring their every move.

Because such surveillance is inexpensive, the resource constraints that have limited other dragnet-type searches do not apply, and the prospect of sweeping surveillance is real.

In fact, for many of us, the government does not even need to go to the trouble of attaching a GPS device.

We already carry them voluntarily. Smartphones use GPS-like technology to transmit to cellular service providers the location of the phone at all times, and therefore the location of the owner as long as he or she is carrying the phone.

Many newer cars feature OnStar, a GPS-based service that tracks the car’s precise location so emergency services can be directed in case of accident.

The government has argued that it should have free access to all this information as well because having “voluntarily” given the information to our phone company or to OnStar, it’s no longer private, and several courts have agreed.

In short, Big Brother has arrived, and we have invited him in. GPS and smartphone devices help us find our way to new restaurants, but they also help the government come along for the ride.

Should our embrace of these modern conveniences mean that we forfeit our right to relative anonymity when we travel in public?

When the Fourth Amendment was adopted, people could reasonably expect that their every movement in public would not be recorded automatically and made available to the government without cost.

If we are to retain some semblance of that privacy today, a warrant and probable cause should be required when technology permits the state, with little or no human intervention, to conduct round-the-clock surveillance against us.

As Justice Stephen Breyer said recently to the government’s lawyer, “If you win, you suddenly produce what sounds like ‘1984.’”

George Orwell might not have been shocked, but James Madison surely would be.

David Cole teaches constitutional law and criminal procedure at Georgetown University’s law center. This column was distributed by The Washington Post, where it first appeared.

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