The U.S. Supreme Court today ruled that law enforcement must obtain a search warrant before accessing location information from cellphone tower sites under the Fourth Amendment. The ruling limits law enforcement's ability to track an individual's movements without a showing of probable cause and is being lauded as a victory for advocates of digital privacy.

In a 5-4 opinion handed down today, the U.S. Supreme Court ruled that law enforcement must obtain a search warrant in order to access cell site location information, which is automatically generated whenever a cell phone connects or “pings” to a cell tower and is stored by wireless carriers for years. The ruling updates Fourth Amendment protections for the digital era.

Prior to today's ruling, law enforcement was able to contact wireless providers and obtain digital data that gave the location of a suspect at any given time without first having to make a showing of probable cause to a magistrate judge in order to get a search warrant. With unfettered access to such data, law enforcement could use the information to place a suspect at the scene of a crime without the guarantees of constitutional protections against unwarranted search and seizures.

The underlying case concerned a defendant who was convicted in several armed robberies at Radio Shack and T-Mobile stores in Ohio and Michigan with the help of past cell phone location data that linked him to the crime scenes.

The issue appeared to have bi-partisan support among the justices. During arguments in the case in December, liberal Justice Sonia Sotomayor alluded to fears of “Big Brother,” the all-seeing leader in George Orwell's dystopian novel “1984,” while conservative Chief Justice John Roberts, who wrote today's majority opinion, stated, “We decline to grant the state unrestricted access to a wireless carrier's database of physical location information.”

Read the Supreme Court's decision here: Carpenter v. United States