A US Appellate Court has ruled that police must obtain a warrant before collecting cellphone location data, finding that acquiring records of what cell towers a phone connected to and when it was connected to them constitutes a Fourth Amendment search. This ruling, from the 11th Circuit, is in opposition to a ruling made nearly a year ago by a separate appellate court. While this ruling won't overturn that one because of their separate jurisdictions, it adds critical precedent to a privacy question that's still far from decided across the country.

The issue is still being decided across the country

In its reasoning, the court notes that while the Fourth Amendment has traditionally been applied to property rights, it's gradually expanded to protect much more, including communications. "In the 20th century, a second view gradually developed," the court writes, "that is, that the Fourth Amendment guarantee protects the privacy rights of the people without respect to whether the alleged 'search' constituted a trespass against property rights."

In particular, the court cites a Supreme Court ruling that found that tracking a person using a GPS unit installed in their car requires a warrant. Even though the location data of a cell site can only place the person holding the phone within a certain range, the court feels that that range is still quite detailed. In the case at hand, cell site data was used to place the defendant near the location of several robberies.

"While committing a crime is certainly not within a legitimate expectation of privacy, if the cell site location data could place him near those scenes, it could place him near any other scene," the court writes. "There is a reasonable privacy interest in being near the home of a lover, or a dispensary of medication, or a place of worship, or a house of ill repute."

The parallels between this case and the GPS case are not exact, however, and it remains to be seen how most jurisdictions will interpret phone location data. In its ruling last year, the Fifth Circuit said that such data was no more than a business record that belongs to phone carriers and is therefore not protected. It said that people who want to see it protected should lobby Congress to do something about it.

The 11th Court dismisses cell carriers' ownership of the records by citing precedent on the matter, stating that carriers' customers do have an expectation of privacy because, quite simply, someone placing a phone call likely only expects that the phone carrier knows what numbers they dialed, and not a slew of additional information. Because of this, the court says that someone making a phone call is not voluntarily exposing their location to a carrier and giving up their expectation of privacy.

The American Civil Liberties Union was involved in arguing that the Fourth Amendment protected cell site location data and says that the court agreed in full with its arguments. "The court’s opinion is a resounding defense of the Fourth Amendment’s continuing vitality in the digital age," ACLU attorney Nathan Freed Wessler says in a statement. "The court soundly repudiates the government’s argument that by merely using a cell phone, people somehow surrender their privacy rights."