Constitution Daily

Smart conversation from the National Constitution Center

Supreme Court Justices broaden cellphone privacy

June 22, 2018 by Lyle Denniston


Voicing computer-age worry about Americans’ privacy when they use their telephones, a sharply split Supreme Court ruled on Friday that the locations where people make or answer calls are protected by the Constitution.  Even as it insisted it was acting narrowly, and spoke of some limits on the reach of the ruling, the Court definitely gave a modern cast to the Fourth Amendment, now 227 years old.

The decision divided the Court 5-4, and the disagreement was so wide that each of the four dissenters wrote separate opinions that together ran four times longer than the relatively brief majority opinion written by Chief Justice John G. Roberts, Jr., and joined by the four most liberal Justices.

Relying on a 1967 ruling that said the Fourth Amendment protects an individual’s “reasonable expectation of privacy,” if that expectation is recognized by society as a whole, the majority declared that – in general – law enforcement officers must get a court-approved warrant before they may gather data from cellphone towers showing where an individual was using a phone.

The ultimate conclusion meant two things constitutionally:

First, a government demand for user data from a company running a cellphone network definitely is a search, governed by the Fourth Amendment.

Second, law enforcement officers must get a search warrant to demand cellphone location data from the network provider. 

The Chief Justice, in insisting that the decision was “narrow,” suggested that it might not apply in times of actual emergency, such as a national security or foreign affairs crisis, and did not disturb the regular use by police of at least some electronic surveillance devices, such as security cameras.

In reaching the decision, the majority turned aside a plea by the federal government to reject cellphone tower records privacy by relying upon two prior rulings, in 1976 and 1979, that had declared that when a person uses a telephone, the records of such calls are the property of the company, not the customers.

While reaching back to a part of the Bill of Rights, from 1791, the Court said it was dealing with “a new phenomenon: the ability to chronicle a person’s past movements through the record of his cellphone signals.”  The opinion noted that this kind of electronic tracking was much like the use of satellite tracking technology, which the Court had ruled in 2012 required a search warrant.

What a cellphone tower gathers from users, the opinion said, is information that is “detailed, encyclopedic, and effortlessly compiled.”

In fact, in the case before the Court involving a Detroit man convicted of a series of store robberies, police access to tower data “clinched the case” because it placed his cellphone being used near several of the stores, according to the Chief Justice’s opinion.

When Timothy Ivory Carpenter appealed his conviction, relying on his claim of a violation of his right to privacy under the Fourth Amendment, a federal appeals court ruled that he had no expectation of privacy because he had shared his location voluntarily with the wireless phone companies operating the nearby towers.  That court relied on the prior Supreme Court precedent declaring that telephone records belong to the company, not the telephone user.  Friday’s ruling reversed that decision.

The decision noted that there are 396 million cellphone service accounts in the United States, for a nation of 326 million people.  When a cellphone is used, the device continuously scans the area where it is used for the best signal, with most modern cellphones linking to a wireless network several times a minute.  Actual use of the phone, to make or receive a call, creates a record that shows the date and time and the location.

The feature of the modern cellphone that was the key to the Court’s decision was this location data, because tracking for any significant period of time can create a map of the user’s travels, just as a GPS device does.  Because the Court has previously made clear that such an array of information about travels implicates a person’s right of privacy in their movements, Friday’s ruling brought such a data map under the Fourth Amendment umbrella of protection.

The decision provided at least some guidance to lower courts as they weighed future cases to decide whether a demand by police or federal agents for cellphone location data would require a search warrant.   Aside from possible situations of an emergency or a case of pursuing a fleeing suspect, the opinion suggested that courts should keep in mind the need to check excessive government power.

Two limitations, it indicated, come from “understandings” at the time the Constitution was written: first, that privacy must be protected against “arbitrary power,” and, second, that intrusions by government into privacy are invalid when they are “too permeating.”

The decision did not spell out further either one of those limitations, but the overall argument made by the Chief Justice’s opinion indicated that the restrictions will be enhanced as changes in technology give the government new ways to enter peoples’ private lives.   Modern devices, it noted, enable the police to enhance their own senses beyond mere visual observation of personal actions.

Turning to the new technology of smartphones, the opinion commented that prior decisions refusing to extend privacy to telephone records had not imagined “a society in which a phone goes wherever its owner goes, conveying to the wireless carrier not just dialed digits, but a detailed and comprehensive record of the person’s movements.”

So, it concluded, it was time to declare that “an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through [data from cellphone towers].  The location information obtained from Carpenter’s wireless carriers was the product of a search” under the Fourth Amendment.

It added: “A cellphone faithfully follows its owner beyond public thoroughfares and into private residences, doctor’s offices, political headquarters, and other potentially revealing locales.”

A significant facet of cellphone location data, the Court said, is that it can look backward, to reconstruct past movements in a way that traditional ways of police surveillance never could.

While the majority expressed the most concern about location information that stretched over “a very long period,” because of the potential breadth of that data, it did not set a time limit on the use of a search warrant demanding such data from the telephone service company.  In Carpenter’s case, it noted, such data spanned 127 days, providing “an all-encompassing record” of the whereabouts of the phone user.

Putting that much data together with other information the police had, the Court said, allowed the officers to “deduce a detailed log of Carpenter’s movements, including when he was at the site of the robberies.”  At his trial, prosecutors relied on those findings in making their closing argument to the jury, the opinion pointed out.

The Chief Justice’s opinion had the support of Justices Stephen G. Breyer, Ruth Bader Ginsburg, Elena Kagan and Sonia Sotomayor.

Among the four dissenting opinions, the one by Justice Anthony M. Kennedy was the one that departed the least from the majority.  He conceded that the government should not always be able to obtain records that are been given by an individual to a third party, such as a business firm, and suggested that a warrant might be required if it were seeking data personally identified with a specific individual.

Three other Justices – Samuel A. Alito, Jr., Neil M. Gorsuch and Clarence Thomas – based their protests largely on arguments that traditional property law concepts should apply, suggesting that cellphone users did not have a personal property claim to the location data.

Legendary journalist Lyle Denniston has written for us as a contributor since June 2011 and has covered the Supreme Court since 1958. His work also appears on


Sign up for our email newsletter