In what civil liberties groups hope will lead to an end of unchecked cell phone tracking of U.S. residents, a federal court of appeals has ruled that law enforcement agencies cannot obtain a person’s historical cell phone location information from cell phone companies without a legal warrant signed by a judge.

In a decision that is likely to propel the issue to the U.S. Supreme Court, the 4th Circuit of Appeals on Wednesday ruled the practice of tracking individuals using information stored on a person's phone or within a company's database system without court approval is an unconstitutional violation of the Fourth Amendment's guarantee against unreasonable search and seizure.

As The Intercept reports:

The decision is the strongest assertion of the Fourth Amendment rights of mobile phone users out of three appellate court decisions on the matter, setting up a likely Supreme Court hearing. “The tide I think is turning,” said Hanni Fakhoury, a senior staff attorney with the Electronic Frontier Foundation, which joined a friend-of-the-court brief in the case of Aaron Graham, a man convicted of armed robbery after his cell phone location information over seven months was obtained by the government from Sprint. The Fourth Circuit Court of Appeals ruling rejected the “third party doctrine,” a legal theory that private information held by a company is not protected by the Fourth Amendment’s prohibitions [...]

Nathan Freed Wessler, a staff attorney with the ACLU, called the opinion "a full-throated defense of Fourth Amendment privacy rights in the digital age."

In previously heard challenges, the two other appeals courts which reviewed the issue—both the 5th and 11th Circuits—ruled differently than the 4th Circuit as they took the side of government lawyers who argued that cell phone users should have no expectation of privacy when their cell phone data is already in the hands of their phone company.

But as Wessler explains, the historic legal idea of the "third party doctrine" should no longer apply in an era when our phones can reveal so much about our personal lives. "Cell phone location records can reveal some of the most private details about our lives by showing where we go and who we spend time with. Requiring a warrant for access to this information is an important protection against unjustified government intrusions."

Cell phone location records can reveal some of the most private details about our lives by showing where we go and who we spend time with. Requiring a warrant for access to this information is an important protection against unjustified government intrusions."

And the court agreed with that position. As the ruling itself stated, "We cannot accept the proposition that cell phone users volunteer to convey their location information simply by choosing to activate and use their cell phones and to carry the devices on their person. Cell phone use is not only ubiquitous in our society today but, at least for an increasing portion of our society, it has become essential to full cultural and economic participation."

However, with discrepant rulings at the appellate court level, it appears as though it will be up to the nation's highest court to weigh in.