The Supreme Court Phone Location Case Will Decide the Future of Privacy

For all of the attention paid to former FBI Director Jim Comey's highly anticipated testimony before the Senate intelligence committee last Thursday, the most important constitutional law development from last week took place across the street (and three days earlier). The Supreme Court agreed to hear argument in Carpenter v. United States later this year—though exactly when, we're not sure.

Carpenter raises a specific question about whether Americans have an expectation of privacy in historical "cell-site location information" ("CSLI"). The petitioner, Timothy Carpenter, was one of two defendants convicted for his role in a series of armed robberies in Michigan and Ohio, based in part on 127 days of CSLI data that placed him between ½ and 2 miles from the robberies around the time they were committed.

On appeal, the Sixth Circuit affirmed his conviction, holding that Carpenter had no expectation of privacy in his CSLI data—and so the government did not need a warrant before obtaining it and admitting it at trial. Whether the Supreme Court endorses or rejects this logic, the answer has enormous implications for privacy rights—and the Fourth Amendment—more generally. Indeed, it's no exaggeration to suggest that Carpenter will be the most important Fourth Amendment case that the Supreme Court has heard in a generation.

A quick refresher on the Fourth Amendment to the Constitution: that's the one that protects individuals from "unreasonable searches and seizures," and says warrants must be issued with "probable cause," and specify a particular area or domain to be searched. As the Supreme Court has interpreted it, the Fourth Amendment applies to a government search—and the warrant requirement is usually triggered—whenever the search intrudes upon a "reasonable expectation of privacy." Thus, whether we have such an expectation of privacy in particular types of property or information is typically the key to whether the Fourth Amendment applies to government actions against the same.

At the heart of the dispute in Carpenter is the "third-party doctrine," the idea that we surrender our constitutional expectation of privacy whenever we voluntarily share non-content information with third-parties, such as our phone companies, internet service providers, financial institutions, and so on. The third-party doctrine brings together two distinct strands of Fourth Amendment theory—that individuals' voluntary conduct can effect a form of "consent" to government searches, and that individuals cannot assert a privacy interest in property they no longer own or possess.

Without an expectation of privacy in such information, the government may collect it without having to satisfy the Fourth Amendment—even if, in some cases, it must nevertheless satisfy more modest statutory requirements that Congress has imposed. Thus, although Edward Snowden's 2013 disclosure of the bulk telephone metadata collection prompted substantial public debate over the constitutionality of such surveillance, it is difficult to see the argument that it was unconstitutional, thanks to the third-party doctrine (the Second Circuit instead invalidated it on narrower, statutory grounds).

Although the phone records program is perhaps the most prominent example, there are hundreds of other government surveillance programs or protocols, the legitimacy of which is predicated on the third-party doctrine.

But as the Snowden disclosures also underscored, technology has dramatically changed the privacy implications of the third-party doctrine. As Justice Sonia Sotomayor explained in a 2012 concurrence,

This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks. People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers.

Not only has technology changed both the quality and quantity of the data we voluntarily provide to third parties (and, perhaps, the extent to which such actions really are "voluntary"); it has also dramatically increased the government's ability to collect larger percentages of such data, to aggregate the collected data from different sources, and to mine the aggregated data for pre-determined selectors, including specific individuals, types of transactions, or other physical or transactional patterns.

So not only are we sharing far more data with third parties than we did in the 1970s (when the third-party doctrine was articulated), but the government is in a far better position today to use that data to obtain information about us that we might not want it to have.

CSLI is a textbook example of this phenomenon. When the Supreme Court first set out the parameters of the third-party doctrine, phone records could often place an individual in their home or office when they were making and receiving telephone calls, but not otherwise or elsewhere. CSLI, in contrast, is the phone company's data of which cellular towers its customers are "pinging" when they're using their cell phones for almost any purpose (and, much of the time, even when they're not), data that can, depending upon the circumstances, be used quite accurately to pinpoint the specific locations of specific individuals at specific times—and not just in their home or office. (When customers have activated the GPS on their phones, the tracking of their location is even more accurate.)

"Historical" CSLI—the data at issue in Carpenter—is when one customer's CSLI is aggregated over time to study their patterns of movement—to follow them, in effect, by following the cell towers being utilized by their cell phone. If, as the lower courts concluded in Carpenter, we have no expectation of privacy in historical CSLI, then the government could theoretically keep near-constant tabs on every American who uses a cell phone—a rather Orwellian proposition, even by today's standards. In addition to the constant surveillance issue, the technology could also track us within our homes—traditionally the most private of places.

To be sure, there is substantial debate over the numerous alternatives to the third-party doctrine, and exactly where courts should draw the line between when we do have an expectation of privacy in information like historical CSLI, and when we do not.

But the Supreme Court's decision to grant certiorari in Carpenter suggests, at the very least, that the Justices are interested in asking—and answering that question. Right now, we don't have any good indications on how they might rule. In Jones, a 2012 case on whether police could attach a GPS tracker to a car without triggering the Fourth Amendment, the Supreme Court unanimously answered that question in the negative, but disagreed as to exactly why. Complicating matters further, Justice Antonin Scalia (who wrote the majority opinion in Jones) has been replaced by Justice Neil Gorsuch—whose vote may well be decisive.

But however the justice vote in Carpenter, the implications for Fourth Amendment jurisprudence—and for the relationship between new technology and constitutional understandings of privacy—will be profound.

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