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Yesterday the Sixth Circuit Court of Appeals issued an unfortunate and legally incorrect holding that the Fourth Amendment provides no protection against warrantless cell phone tracking. Although couched in language stating narrowly that the Constitution does not protect criminals鈥� 鈥渆rroneous expectations regarding the undetectability of their modern tools,鈥� the impact of the opinion sweeps far more broadly, holding that the innocent as well as the guilty lack Fourth Amendment protection in cell phone location information. This is wrong, for a number of reasons.

The defendant in the case is one Melvin Skinner, who was allegedly involved in a marijuana trafficking operation of epic proportions. After a complex investigation by the Drug Enforcement Administration, Skinner was busted while in possession of over 1,100 pounds of marijuana. The DEA tracked Skinner down in part by obtaining various kinds of location tracking data for the cell phone he was using: cell site information, GPS real-time location, and 鈥減ing鈥� data. Law enforcement agents appear to have tracked Skinner鈥檚 movements using this information for about three days.

The ACLU has argued repeatedly that the Fourth Amendment provides protections against warrantless cell phone tracking, particularly continuous tracking over prolonged periods of time such as the three days at issue in Skinner鈥檚 case. The Fourth Amendment protects people鈥檚 reasonable expectations of privacy, and people reasonably expect that they will not be subject to this invasive form of surveillance. That is because location data is very sensitive, revealing private facts. As an appeals court has :

A person who knows all of another鈥檚 travels can deduce whether he is a weekly church goer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups鈥攁nd not just one such fact about a person, but all such facts.

That is not to say that law enforcement agents can never obtain cell phone location data. The question, rather, is under what circumstances they are permitted to do so. Because of the privacy interests at stake, law enforcement should have to go to a judge and get a warrant, which involves proving that they have probable cause to believe that tracking location would turn up evidence of a crime. There are numerous police departments that get a warrant for cell phone tracking, and it鈥檚 the best way to ensure that law enforcement can do its job while also protecting Americans from having their privacy needlessly invaded.

Unfortunately, that is not the conclusion drawn by the Sixth Circuit. The majority practically scoffed at the idea that Melvin Skinner had any reasonable expectation of privacy in 鈥渄ata emanating鈥� from his cell phone. This passage best captures the court鈥檚 view that Skinner鈥檚 claim to constitutional protection was the height of audacity:

The law cannot be that a criminal is entitled to rely on the expected untrackability of his tools. Otherwise, dogs could not be used to track a fugitive if the fugitive did not know that the dog hounds had his scent. A getaway car could not be identified and followed based on the license plate number if the driver reasonably thought he had gotten away unseen.

In other words, a person鈥檚 ignorant belief that he has made a clean getaway does not shield him from detection.

But this is not the right question. The mere fact that the police are capable of tracking someone doesn鈥檛 mean they鈥檙e entitled to do so without first getting a warrant, any more than the mere fact that it鈥檚 easy to break down someone鈥檚 front door or open their postal mail gives the police the right to take these steps without a warrant. The question, rather, is whether a police action invades a person鈥檚 reasonable expectation of privacy that society is prepared to recognize as reasonable. Because people reasonably expect privacy in their movements, as the D.C. Circuit explained in the passage above, the Fourth Amendment provides us with protection.

If a suspected criminal鈥檚 phone can be tracked without a warrant, then all of our phones become tracking devices that the government can use to monitor us for any reason or no reason at all.

The Sixth Circuit was able to reach the conclusion that it did by relying on a 25-year-old Supreme Court case dealing with a more primitive tracking technology known as a 鈥渂eeper.鈥� In the beeper case, United States v. Knotts, the police used a combination of visual surveillance and signals from the beeper to track an investigative target as he traveled on public roads. The Supreme Court approved the tracking in Knotts, and the Sixth Circuit found that the DEA鈥檚 tracking of Skinner was not meaningfully different:

Similar to the circumstances in Knotts, Skinner was traveling on a public road before he stopped at a public rest stop. While the cell site information aided the police in determining Skinner鈥檚 location, that same information could have been obtained through visual surveillance. There is no inherent constitutional difference between trailing a defendant and tracking him via such technology.

This is really the heart of the matter. The Sixth Circuit鈥檚 fundamental error is in believing that a technological change that makes it vastly more feasible to track us all in great detail, continuously, and at little cost is simply irrelevant. It is not irrelevant. It is highly significant. Physically tailing a person for days on end requires a mass commitment of resources, which in turn limits the possibilities for abuse. The police aren鈥檛 going to enlist huge numbers of people for a massive surveillance operation without a very good reason. But when a single police officer can achieve the same level of surveillance using GPS, all while sitting at his desk and flipping open a laptop, the situation is radically transformed. As the invasiveness of tracking and the ease of tracking increase, the supervision of courts applying meaningful constitutional standards become all the more important.

The Sixth Circuit is the first court of appeals to address the Fourth Amendment and cell phone tracking after the Supreme Court鈥檚 decision in that when the police attach a GPS device to a car, that is a search under the Fourth Amendment. But Jones will be of little value if the police can simply track cell phones instead of cars and, with the Sixth Circuit鈥檚 decision holding that they can indeed do so, we鈥檙e off to a bad start. The Fifth Circuit is poised to consider the same issue later this year and has scheduled argument for October. Let鈥檚 hope that it鈥檚 more sensitive to the privacy interests at stake than its sister circuit.