Brian Snyder / Reuters

Yet another U.S. appeals court—the Fourth Circuit, this time—has affirmed that it is completely legal for authorities to track your cellphone without a warrant. That is, law enforcement can ask a cell provider for a list of everywhere a certain phone has been during a certain time period (perhaps hundreds of days) and receive the list of points quickly and freely—and without ever notifying the tracked person.

The Sixth Circuit also affirmed the legality of CSLI tracking last month. Back then, I wrote about how specific this kind of location tracking can get:

[CSLI] isn’t as precise as a GPS coordinate, but in urban or suburban areas it can narrow someone’s location down to less than two miles and give their angular relationship to the nearest cell tower. String a set of these time-stamped points together and you can disprove an alibi or reconstruct an escape route.

Judge Diana Gribbon Motz wrote the majority opinion for the Fourth Circuit. One part of her decision stood out to me. After issuing an initial finding, she spends some time on the defendants’ claim that cellphone users do not voluntarily convey their location to cell providers. Instead, defendants say, cell providers generate this data themselves and customers remain ignorant of the whole process.

In making this claim, the defendants are seeking to apply a legal idea called the “third-party doctrine” to CSLI tracking. The third-party doctrine was originally developed in the 1970s for situations like telephone landlines. It asserts that someone who, for instance, dials a phone number has no claim to the privacy of that number, because they voluntarily surrendered it when they “conveyed” the number to the phone company. Under the law, cops can obtain that phone number without seeking a warrant first—the gathering doesn’t count as a search under the Fourth Amendment. (If they wiretap the phone, they still need a warrant.)

Judge Motz, therefore, has to prove that cellphone users voluntarily convey their location information to cell providers. So she steps back. Think about how cellphones work, she says—they require a hyper-awareness of location from their users. She writes:  

When an individual purchases a cell phone and chooses a service provider, he expects the provider will, at a minimum, route outgoing and incoming calls and text messages. As most cell phone users know all too well, proximity to a cell tower is necessary to complete these tasks. Anyone who has stepped outside to ‘get a signal,’ or has warned a caller of a potential loss of service before entering an elevator, understands, on some level, that location matters. […]

A cell phone user voluntarily enters an arrangement with his service provider in which he knows that he must maintain proximity to the provider’s cell towers in order for his phone to function. […] Whenever he expects his phone to work, he is permitting—indeed, requesting—his service provider to establish a connection between his phone and a nearby cell tower. A cell phone user thus voluntarily conveys the information necessary for his service provider to identify the CSLI for his calls and texts. And whether the service provider actually “elects to make a … record” of this information “does not … make any constitutional difference.”

Motz is making a legal argument by way of technological folk saying, suggesting that the popular understanding of cellphones compels popular complicity with the creation of CSLI. Americans know when their cell signal is breaking up, therefore Americans must know that their cellphone company can track them. Call it the Can you hear me now? theory of privacy.

Except, it isn’t necessarily true. There are plenty of technologies that rely on physical proximity but that do not permit a geographic record to be made of their users’s location. The prime example of this? Your car radio, which also depends on towers and antennae, and which you can also “lose service” depending on your whereabouts. Any kind of portable radio follows this principle, too: Physical proximity determines whether you can hear a radio station or not (or broadcast on it, for short-wave), but, again, there’s no expectation that listening to a signal means you’re surrendering your geographic location. And while it is possible to deduce a radio signal’s location from its signal, that would require special equipment and expertise. (And to extend the cellphone analogy, that signal-sniffing technology is much more closely related to the meager and undeveloped law around Stingrays.)

And not all of the precedents concern audio. The global positioning system is designed in such a way that you can figure out where you are on the planet without ever alerting anyone else to your location. (Your receiver “listens” to the three nearest GPS satellites and triangulates its location accordingly.) In other words, the signal-dependent technology that would most seem to require conveyance of your physical location—it has global positioning system in its name!—in fact doesn’t.

The existence of GPS, radio, and walkie-talkies does not necessarily invalidate Motz’s reasoning. As she herself writes, it doesn’t matter whether cell providers choose to make a record of someone’s location—as long as they can. But I question whether the phrases we all say about cellphones—“About to go into a weak spot for service, call you back!”—indicate that people expect cell towers to ​know where they are. The folk sayings surrounding a technology shouldn’t shape the Constitutional law around its use. There are plenty of proximity-dependent technologies that never permit the creation of a kind of data like CSLI. The Verizon guy may seem like a nice dude, but he’s not an friend of the court.

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