Phone Tracking Should Require a Warrant

By Susan Freiwald, Professor of Law, USF School of Law, and Peter Swire, C. William O'Neill Professor of Law, the Ohio State University.

A pending case in the 3rd Circuit U.S. Court of Appeals raises a profound question -- should the government be able to track your location without a warrant? Not so long ago, few of us carried cell phones. Today, the vast majority of Americans does. At stake are the rules for tracking the location of cell phones and their owners.

In the pending case, the Department of Justice appeals a ruling that prohibits it from compelling the disclosure of Cell Site Location Information (CSLI) without a probable-cause warrant. Our view is simple (even though the underlying technology is complex): law enforcement agents must get a warrant before they may compel your cell phone provider to disclose this location information.

What is CSLI?

That's a key question. Cellular providers could, if they wanted, keep track of your cell phone's location every seven seconds, because your phone "registers" that often with the nearest tower. That way the system knows where to deliver your calls. Is detailed information about the subscriber in CSLI? Can agents triangulate from the data -- can they pinpoint your location using data from multiple towers, signal strength and angle, GPS data and the like? The government says that it is only asking to know which tower (and which tower face) was nearest to your phone when you made and received calls. It argues that a Supreme Court precedent (from the 1980's) that permitted cops to track a car on public roads (using a radio beeper) without a warrant applies here because CSLI is just as imprecise.

We would say (and in an amicus brief one of us did) that the more applicable (1980's beeper) precedent required a warrant because agents could figure out when the target was home. Also, EFF, ACLU, ACLU of PA, and CDT (online civil liberties groups) filed an amicus brief that showed that prosecutors use CSLI to infer such private information as when the target is at home, which, under a 2001 precedent, requires a warrant.

Bottom line: we really don't know what CSLI is, because we don't know:

• what information the cell phone providers keep (they don't tell us and it likely varies);
• what information the government requests (the records show conflicting information); and
• what information providers give when asked (they may just dump data rather than filtering data).

For that reason, we think the 3rd Circuit should take account of what CSLI can include because that is likely what the government willget. Because the subscriber whose CSLI is sought will not know beforehand, if ever, the court has to oversee the process. That happens if the 3rd Circuit upholds the warrant requirement, but not if it doesn't.

What Do the Fourth Amendment Precedents Say?

It depends - individuals have historically not carried tracking devices such as cell phones. We've mentioned the beeper cases. But the DOJ also relies on a Supreme Court case from the 1970's. In that case, cops used a subpoena (less strict than a warrant) to access a customer's bank records (account statements, deposit receipts). The government claims that because they could get historical CSLI data from a provider's records, they may avoid the probable cause requirement and all the judicial oversight that goes along with it. The government argues it should merely be required to establish that the information it seeks is relevant to an investigation, which effectively means it can grab data even for those not suspected of a crime. (Can you say "fishing expedition"?)

This stuff is complicated, as we warned, but we question the precedent itself (as based on faulty reasoning) and argue that in any case acquiring CSLI is quite different from subpoenaing bank records. As the magistrate judges described well in their decision, CSLI discloses intensely private information (like that you go to AA meetings, went to an abortion clinic, protested American foreign policy...). In her amicus brief, one of us argued that because CSLI acquisition is hidden, indiscriminate and intrusive, and because it reveals information over a period of time, it should be subject to the highest level of Fourth Amendment oversight (the same procedures used for wiretapping and video surveillance).

Will the Court Even Reach the Fourth Amendment Question?

Maybe not. The court may avoid it if it accepts the government's claim that it seeks information too imprecise to implicate the Fourth Amendment. As discussed, were the court to approve the government's request (but just as to a limited subset of CSLI), that may not prevent the government from actually seeing much more. Requiring a warrant would be much better because it would afford notice to the target and after-the-fact review by a court.

The Court may also avoid the constitutional question by construing the applicable statute (the Stored Communications Act) to grant the judge discretion to require a warrant. The EFF/ACLU/CDT brief advocated that approach (as well as arguing for a Fourth Amendment analysis) and constitutional avoidance doctrine supports it too. Getting into the details of the argument, however, would take a blog post that is at least twice as long.

We hope the court affirms the lower court decision on Fourth Amendment grounds and requires a probable cause warrant for CSLI access, whenever it is gathered, and whatever it contains. Let Congress go back and fix the more than 20-year-old statute, which desperately needs updating to adequately protect new communications technologies. If the 3rd Circuit could bring clear guidance and a simple rule to this unduly complicated analysis, that would be a welcome development indeed.