This past week, the United States Supreme Court heard oral argument in Carpenter v. United States, a case that goes to the heart of the government’s power to track private individual behavior without a warrant. Timothy Carpenter and his henchmen had engaged in a series of armed robberies in Michigan and Ohio that led to his conviction for up to 116 years in prison. In his opinion, Judge Raymond Kethledge of the Sixth Circuit correctly observed that the Fourth Amendment’s protection against unreasonable searches and seizures “has long recognized a distinction between the content of a communication and the information necessary to convey it. Content, per this distinction, is protected under the Fourth Amendment, but routing information is not.”

Accordingly, Kethledge let the government introduce into evidence the business records from the defendants’ wireless carriers that placed the defendants at or near the scene of several violent robberies. Alone, that evidence could never support a conviction for armed robbery, but its value lies in contravening the defendants’ alibi that they were elsewhere at the time.

Kethledge’s analysis received a rocky reception at the Supreme Court, as both liberal and conservative’s fretted about the invasions of privacy from such extended surveillance. A puzzled Justice Stephen Breyer professed astonishment by observing: “This is an open box. We know not where to go.” In contrast, Justice Elena Kagan had a more pointed objection. She noted that in United States v. Jones (2012), the Court reversed a conviction for narcotics trafficking because the government had conducted an illegal search by attaching a GPS tracking device to the defendant’s wife’s car without a warrant. According to the majority in that case, attaching the GPS amounted to a common law trespass, which Justice Antonin Scalia held justified suppressing that evidence. To Kagan, the government had to explain how using phone company records differed from using the GPS system, when both give exhaustive and accurate information about the defendant’s whereabouts.