In a landmark decision, the 11th US Circuit Court of Appeals unanimously ruled (PDF) yesterday that law enforcement officials need to have a warrant to access mobile users' phone location data.

The decision stems from the case of Mr. Quartavius Davis who was sentenced to almost 162 years behind bars for taking part in a string of armed robberies. The evidence against him included his mobile phone location data, as well as calls made and received by his phone, that confirmed his proximity to the robbery sites at the time the crime occurred.

As the law enforcement agency didn't obtain warrants before procuring Davis' phone location data, he appealed against the conviction saying the procurement violated his Fourth Amendment right. The court agreed with him.

Although the Stored Communications Act permits law enforcement agencies to access data with a warrant or court order, the appeals court deemed that a court order, which law enforcement officials used in this case, isn't sufficient.

"We hold that cell site location information is within the subscriber's reasonable expectation of privacy. The obtaining of that data without a warrant is a Fourth Amendment violation", the judges said in their decision.

Although the 11th Circuit covers only Florida, Georgia, and Alabama, the ruling could set a precedent across the nation. The decision, however, didn't affect Davis' case, as the court still upheld his conviction by allowing the phone location data to continue to be included in the case.