On Tuesday a federal appeals court ruled that police do not need a warrant to obtain historical location data from cellphone companies because the Fourth Amendment does not protect such information. The U.S. Court of Appeals for the 5th Circuit concluded that the Supreme Court's "third party doctrine," which holds that people have no reasonable expectation of privacy in information they voluntarily disclose to others, applies to cellphone geolocation data, despite the wealth of personal details they can reveal. That means such records have only as much protection as Congress or state legislatures choose to provide. The 5th Circuit's decision comes less than two weeks after the New Jersey Supreme Court ruled, based on the privacy clause of that state's constitution, that police generally do need a warrant to obtain cellphone location data. This is the first time a federal appeals court has squarely addressed the issue.

Under the Stored Communications Act, law enforcement agencies can obtain court orders requiring production of cellphone records based on "specific and articulable facts showing that there are reasonable grounds to believe" the records are "relevant and material to an ongoing criminal investigation." Under the Fourth Amendment, the standard for a search warrant is stricter: "probable cause" to believe that evidence of a crime will be discovered. The case heard by the 5th Circuit involved three applications for court orders covering two months of cellphone location information for specific customers. The court was asked to decide whether the "specific and articulable facts" standard is constitutionally deficient.

No, it is not, the court decided, because the Fourth Amendment does not apply to cellphone location data, which are just another example of the "business records" that the Supreme Court has said can be perused by the government at will in the absence of statutory restrictions. After all, the court reasoned, people should know by now that connecting their wireless calls requires transmitting their locations to their cellphone companies. Since no one is forced to use a cellphone, anyone who chooses to do so is voluntarily disclosing his whereabouts to a third party, thereby losing any reasonable expectation of privacy in that information.

According to this logic, people are not allowed to share information with others for limited purposes and still retain Fourth Amendment protection against government snooping. It's all or nothing. Buy a cellphone, and you automatically consent to having the government track your every move (except when prohibited by statute). You cannot opt out. And once this line of reasoning catches on, it will become a self-fulfilling prophecy, since people living under a government that has such broad surveillance powers cannot reasonably expect that their comings and goings will remain private.

The 5th Circuit's decision sits uneasily with U.S. v. Jones, the 2012 decision in which the Supreme Court said tracking a suspect's car by attaching a GPS device to it amounts to a "search" under the Fourth Amendment. Although the majority opinion in Jones hinged on the physical intrusion required to install the device, five justices expressed the view that the breadth of information generated by tracking someone's car for a month was enough to trigger Fourth Amendment protection. If you have a reasonable expectation of privacy in the whereabouts of your car for the last month, surely you have a reasonable expectation of privacy in the whereabouts of your cellphone for the last two months. The 5th Circuit declined to draw that inference:

[Supreme Court] precedent, as it now stands, does not recognize a situation where a conventional order for a third party's voluntarily created business records transforms into a Fourth Amendment search or seizure when the records cover more than some specified time period or shed light on a target's activities in an area traditionally protected from governmental intrusion. We decline to create a new rule to hold that Congress's balancing of privacy and safety is unconstitutional.

Justice Sonia Sotomayor's concurring opinion in Jones, calling upon her colleagues to reconsider the always questionable and increasingly alarming third party doctrine, is looking more perceptive every day. That doctrine makes not just cellphone location data but all sorts of remotely stored information, which nowadays includes a tremendous amount of sensitive material, vulnerable to government snooping unless legislators decide otherwise.

You can read the 5th Circuit's ruling here. Ron Bailey pondered the surveillance potential of cellphones in the January issue of Reason. Last year I asked, "Is That a Spy in Your Pocket?"