A federal appeals court has found no Fourth Amendment violation in the government’s use of cell-site records to establish that two suspects used their cell phones close to the locations of armed robberies in the Detroit area.

The Cincinnati-based 6th U.S. Circuit Court of Appeals upheld use of the evidence in the cases of Timothy Carpenter and Timothy Sanders, convicted under the federal Hobbs Act for aiding and abetting robberies that affect interstate commerce. The court ruled (PDF) on Wednesday that the FBI’s collection of cell-site data was not a search under the Fourth Amendment.

The government had obtained the cell-site information after a magistrate approved the request under the Stored Communications Act. The law requires only that the government have reasonable grounds to believe the requested business records are “relevant and material to an ongoing criminal investigation.” Carpenter and Sanders had argued the FBI should have obtained a warrant supported by probable cause.

The defendants and the American Civil Liberties Union had cited United States v. Jones, a 2012 U.S. Supreme Court decision holding that police conducted a search within the meaning of the Fourth Amendment when they attached a GPS device to a drug suspect’s car.

But the 6th Circuit said the government action in the case against Carpenter and Sanders differs from the government action in Jones. “Whether a defendant had a legitimate expectation of privacy in certain information depends in part on what the government did to get it,” the appeals court said. “A phone conversation is private when overheard by means of a wiretap; but that same conversation is unprotected if an agent is forced to overhear it while seated on a Delta flight.”

In this case the cell-site information was contained in third-party business records, “which can only diminish the defendants’ expectation of privacy,” the appeals court said. The court also distinguished between GPS data—which is accurate within 50 feet—and cell-site data, which only revealed the suspects’ locations within a radius of a half mile to two miles.

ACLU lawyer Nathan Freed Wessler criticized the decision in a statement. “The majority’s opinion unfortunately fails to adequately account for the privacy violations made possible by the cell phones that we all need to carry around to live our lives normally,” he said. “When police obtain months’ worth of cell phone data comprising thousands of individual locations, like they did in this case, they should have to get a search warrant from a judge. … Comprehensive location tracking like this requires robust Fourth Amendment protections.”

Two other federal appeals courts have also held that the government’s use of cell-site records is not a Fourth Amendment search, the Volokh Conspiracy reports.

The case is United States v. Carpenter.