Every move you make: how new surveillance technologies threaten privacy.

• Author: Sullum, Jacob
• Position: Columns - Column

"IF You WIN this case," Supreme Court Justice Stephen Breyer told the Obama administration's lawyer during oral argument in U.S. v. Jones last fall, "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." That prospect, Breyer said, "sounds like 1984."

Fortunately, the government did not win the case. But the Court's unanimous decision, announced in January, may not delay Breyer's 1984 scenario for long. Unless the Court moves more boldly to restrain government use of new surveillance technologies, the Framers' notion of a private sphere protected from "unreasonable searches and seizures" will become increasingly quaint.

The case decided in January involved Antoine Jones, a Washington, D.C., nightclub owner who was convicted of cocaine trafficking based largely on information that investigators obtained by surreptitiously attaching a GPS tracking device to his car. All nine justices agreed a warrant was constitutionally required for this surveillance, but they offered two different rationales.

Antonin Scalia's majority opinion emphasized the intrusion on Jones' car. "The Government physically occupied private property for the purpose of obtaining information," Scalia wrote. "We have no doubt that such a physical intrusion would have been considered a 'search' within the meaning of the Fourth Amendment when it was adopted."

The majority therefore decided it was unnecessary to resolve the question of whether Jones had a "reasonable expectation of privacy" regarding his travels on public roads. Four other justices, in an opinion by Samuel Alito, said he did, given that investigators tracked all his movements for a month--a kind of surveillance that can reveal a great deal of personal information.

While Scalia's approach draws a clear line that cops may not cross without a warrant, it does not address surveillance technologies that involve no physical intrusion, such as camera networks, satellites, drone aircraft, and GPS features in cars and smartphones. If police had tracked Jones by activating an anti-theft beacon or following his cellphone signal, they could have obtained the same evidence without touching his property.

The Court developed the...