San Francisco - The Electronic Frontier Foundation (EFF) joined the American Civil Liberties Union (ACLU) Foundation and the ACLU Foundation of Texas Friday in backing a judge who required a search warrant before approving the seizure of two months of cell phone location data by law enforcement.

In this case, the government asked a magistrate judge to approve a request to two cell phone companies for 60 days of cell phone location records as part of a routine law enforcement investigation. The judge denied the request, saying it was necessary for the government to get a warrant based on probable cause before it could obtain the records. In an amicus brief filed in the U.S. Court of Appeals for the 5th Circuit, EFF argues that the judge was correct, as getting a warrant is essential to ensuring Fourth Amendment protections.

"The Supreme Court ruled earlier this year in United States v. Jones that the GPS tracking of a vehicle without a warrant violates the reasonable expectation of privacy guaranteed by the Fourth Amendment to the Constitution. This is a very similar situation," said EFF Staff Attorney Hanni Fakhoury. "People carry their cell phones with them wherever they go, all day long. Records of where we've been can reveal information about our health, our religion, our hobbies, and our politics. As technology advances, these records will become only more detailed and intrusive."

The government claims that cell phone users voluntarily disclose their physical location to their service provider every time their phone connects to a cell phone tower, meaning they give up their privacy rights under the "third-party doctrine." However, this theory would undermine privacy in nearly any networked communication. In fact, in the Jones case, Justice Sonia Sotomayor expressed concern about the third-party doctrine, writing that it was "ill-suited to the digital age."

"The judge in this case has a right to demand probable cause before allowing access to this sensitive information," Fakhoury said. "This is a powerful tool that police should be able to use in criminal investigations, but only after they can get a warrant based on probable cause."

The Center for Democracy and Technology (CDT) and the National Association of Criminal Defense Lawyers (NACDL) also signed on to Friday's brief.

For the full amicus brief:

For more on cell phone tracking:

Hanni Fakhoury
   Staff Attorney
   Electronic Frontier Foundation