The government is free to attach a GPS device to the car of any American and record that person’s public movements for a month or more without a warrant or suspicion of wrongdoing, a government lawyer told the Supreme Court on Tuesday.

Even the nine justices.

“You could tomorrow decide that you put a GPS device on every one of our cars, follow us for a month. No problem under the Constitution?” asked Chief Justice John G. Roberts Jr.

It is allowed under the court’s own precedents, replied Deputy Solicitor General Michael R. Dreeben, and is no different than if the FBI “put its team of surveillance agents around the clock on any individual and follow that individual’s movements as they went around on the public streets.”

But to many of the justices, something did seem different. In an intense hour-long exchange in which the Big Brother of George Orwell’s novel “1984” was referenced six times, the justices wondered how the dizzying pace of technology has changed a person’s reasonable expectation of privacy.

The justices pondered a world in which satellites can zero in on an individual’s house, cameras record the faces at a crowded intersection and individuals instantly announce their every movement to the world on Facebook. They wondered about the government placing tracking devices in overcoats or on license plates.

“How do we deal with this?” Justice Samuel A. Alito Jr. asked. “Do we just say, ‘Well, nothing is changed,’ so that all the information that people expose to the public is fair game?”

The court is trying to apply the Constitution’s centuries-old protection against unreasonable searches and seizures at a time when devices such as a GPS can essentially do police officers’ work for them.

The court, Dreeben said, has already settled the greater question: “What a person seeks to preserve as private in the enclave of his own home or in a private letter or inside of his vehicle when he is traveling is a subject of Fourth Amendment protection.”

He added: “But what he reveals to the world, such as his movements in a car on a public roadway, is not.”

In 1983, the court ruled in United States v. Knotts that police were within their power to track a car traveling from one state to another with a beeper device they had placed in a can of chemicals used for drug production. “A person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another,” it said.

The case at hand, Dreeben said, is directly analogous. It involves a suspected D.C. drug kingpin named Antoine Jones, who was convicted in part because of evidence gathered from the use of a GPS device placed on his car that tracked his movements on public roads for 28 days.

His conviction was overturned when a panel of the U.S. Court of Appeals for the District of Columbia Circuit said the use of the GPS and extended period of surveillance required a warrant (investigators had obtained a warrant for Jones, but it expired before they attached the device to his car).

Other appellate courts have held that GPS surveillance does not require a warrant.

The justices displayed varying degrees of alarm about the government’s theory. “If you win this case, then there is nothing to prevent the police or the government from monitoring 24 hours a day the public movement of every citizen of the United States,” Justice Stephen G. Breyer said.

Dreeben said the court should hold those concerns for a case in which there was an abuse. “This case does not involve universal surveillance of every member of this court or every member of the society,” he said. “It involves limited surveillance of somebody who was suspected of drug activity.”

He estimated that the number of times federal investigators have used GPS tracking is in the “low thousands.”

But the justices also appeared conflicted about where to draw a constitutional line.

Stephen C. Leckar, representing Jones, said police should be required to persuade a judge to issue a warrant for each use of a GPS device. But the justices wondered how that squared with their previous rulings that no warrant is needed when the person being targeted was being monitored in public places.

“If there is no invasion of privacy for one day, there is no invasion of privacy for 100 days,” Justice Antonin Scalia said.

Alito said Leckar had not shown that using a GPS device was any different from traditional police surveillance.

Dreeben agreed when he made his rebuttal. “The fact that GPS makes it more efficient for the police to put a tail on somebody invades no additional expectation of privacy that they otherwise would have had,” he said.

He told the court that the government’s “fallback” position would be that police need “reasonable suspicion” before using GPS surveillance, a lower legal standard than would be needed to obtain a warrant. But such decisions, he said, would be made by police.

The case is United States v. Jones .