There is a powerful scene in the television adaptation of Margaret Atwood’s The Handmaid’s Tale, where the main character and her husband realize that the United States is crumbling into a authoritarian theocracy. The couple hires a man to help them escape to a safer place, and the man promptly smashes their cell phones.

Such devices, as the Supreme Court explained on Friday, track “nearly exactly the movements of its owner.”

In its 5-4 decision in Carpenter v. United States handed down on Friday, the Supreme Court held that police must first obtain a warrant before they can use cell phone records to track down such fleeing refugees — or, in the moderately less dystopian world we now live in, before they can use that information to track a criminal suspect.

Chief Justice John Roberts wrote the Court’s opinion on behalf of himself and the four liberal justices. The remainder of the Court’s conservative bloc dissented.

Carpenter fits into a larger pattern in the Roberts Court. For the most part, the current Supreme Court isn’t especially friendly to criminal defendants — Carpenter was handed down just minutes after another 5-4 decision reading the Constitution’s Double Jeopardy Clause narrowly. But a majority of the justices appear to recognize that new technology raises unprecedented threats to privacy, and that this technology must be met with a sufficiently robust Fourth Amendment regime.


“As technology has enhanced the Government’s capacity to encroach upon areas normally guarded from inquisitive eyes,” Roberts writes in Carpenter, “this Court has sought to ‘assure[ ] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.’”

Roberts is often perceived as a Luddite. In a 2010 oral argument, he even asked a lawyer, “What is the difference between a pager and e-mail?” To his credit, however, Roberts’ fear of technology appears to have given him healthy concerns about what law enforcement might do with it. The Chief also authored the Court’s decision in Riley v. California, holding that police cannot arrest you and then search through your cell phone without a warrant. And he joined the Court’s opinion in United States v. Jones, which limits law enforcement’s power to track you with a GPS device.

Carpenter, however, is a harder case because it sits precisely at the intersection of two competing Supreme Court decisions — Jones and Smith.

Jones, as Roberts explains, “addresses a person’s expectation of privacy in his physical location and movements.” The general rule that emerges from Jones is that extended tracking of an individual’s movements is not allowed.

At the same time, however, another line of cases draw “a line between what a person keeps to himself and what he shares with others.” The general rule is that “a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties.” Thus, as the Court held in Smith v. Maryland, police can obtain a record of every telephone number you dialed in the last six months, because you voluntarily revealed those numbers to the phone company.


Our cell phones routinely ping nearby cell phone towers and similar sites, often as frequently as several times a minute. Based on this information, cell phone companies can construct a fairly accurate view of everywhere you have been (or, at least, everywhere your cell phone has been) for years.

Carpenter involves long-term tracking of a criminal suspect’s movements. But it also involves records containing information the suspect voluntarily revealed to their cell phone company.

Roberts’ resolves this dilemma in favor of the privacy rights protected by Jones. “Whether the Government employs its own surveillance technology as in Jones or leverages the technology of a wireless carrier,” the Chief writes, “we hold that an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through” cell phone data.

Indeed, Carpenter paints a grim vision of what could happen if the dissenters had prevailed. Cell phone location data “data provides an intimate window into a person’s life, revealing not only his particular movements, but through them his ‘familial, political, professional, religious, and sexual associations.’” Worse, police can gather this information retroactively. And they can target nearly anyone at all.

With access to CSLI, the Government can now travel back in time to retrace a person’s whereabouts, subject only to the retention polices of the wireless carriers, which currently maintain records for up to five years. Critically, because location information is continually logged for all of the 400 million devices in the United States—not just those belonging to persons who might happen to come under investigation— this newfound tracking capacity runs against everyone Unlike with the GPS device in Jones, police need not even know in advance whether they want to follow a particular individual, or when.

Carpenter is not a total victory for privacy. The Court rather ominously notes that it does not “express a view on matters not before us” including so-called “tower dumps,” where police request “a download of information on all the devices that connected to a particular cell site during a particular interval.”


Police, in other words, cannot track a single person’s movements over a long period of time unless they obtain a warrant. But they may be able to take a snapshot of any particular area to see if a specific person was there at a specific time.

For the moment, however, a majority of the Court appears to recognize that old rules — which may have made sense when our telephones were fixed devices in our homes — should not be applied to newer devices that can reveal nearly every about us and how we live our lives.