Chicago—The Electronic Frontier Foundation (EFF) is urging a federal appeals court in Chicago to rule that police need a warrant to access cell phone location records that can reveal our everyday travels—when we leave home, where we go and whom we visit.

In an amicus brief filed Friday in the United States Court of Appeals for the Seventh Circuit, EFF, the American Civil Liberties Union (ACLU), and ACLU of Wisconsin said cell phone location information—data that show where our phones are at a given time and date—generates a comprehensive picture of a person’s movements. Because we carry our phones with us wherever we go, these data can reveal intensely personal information like when we see the doctor, attend a political meeting, or visit friends. Americans have the right to expect that this information remain private and beyond the reach of law enforcement officers unless they first obtain a search warrant.

In this case, U.S. v. Patrick, a Wisconsin man was charged with being a felon in possession of a weapon. Police tracked the man down in real time using location information from his cell phone—obtained either from a phone company or possibly collected using a cell-site simulator, devices known as Stingrays that trick mobile phones into connecting with them. He was located in a car where a gun was found at his feet and arrested. In the brief filed Friday, EFF and the ACLU explain to the court that real-time cell phone location tracking violates the Fourth Amendment’s prohibition against unreasonable search and seizures.

“This is the first time this federal appeals court, whose rulings affect Illinois, Wisconsin and Indiana, is considering whether citizens have an expectation of privacy in real-time cell phone location records,’’ said EFF Senior Staff Attorney Jennifer Lynch. “This case comes as we are seeing a groundswell of recognition that this information is private. Legislatures in the three states covered by the Seventh Circuit have all now prohibited warrantless real-time cell phone. California and at least eight other states also require warrants for real-time tracking.”

There have been conflicting rulings over this issue on the federal level. In 2014 the U.S. Court of Appeals for the Eleventh Circuit in Atlanta ruled that there’s no expectation of privacy in historical cell site location records, so police don’t need a warrant to get them, while the U.S. Court of Appeals for the Fourth Circuit in Richmond, Virginia, last year ruled the opposite.

The U.S. Supreme Court has already recognized that data about where we go can be incredibly revealing and that cell phones hold vast amounts of private information—potentially the sum of an individual’s private life. The court ruled that searching a cell phone found during an arrest and tracking a car using GPS now both require a search warrant.

“The Seventh Circuit should follow the Supreme Court’s lead and recognize that police shouldn’t have unfettered access to records that that can reveal our every move. Law enforcement must be required to get a warrant before accessing the vast amount of private information generated by cell phone location records,’’ said EFF Senior Staff Attorney Adam Schwartz.