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Constitution Check: How private is the place where cellphone calls are made?

February 20, 2014 by Lyle Denniston


Lyle Denniston looks at the police use of cellphone tower information to track the movements of users, an issue that has lower courts split and could be headed to the Supreme Court.


“Cellular telephones are increasingly viewed as necessary to social interactions as well as the conduct of business.  More fundamentally,…cellular telephones physically accompany their users everywhere – almost permanent attachments to their bodies….Many if not most of one’s fellow pedestrians and travelers are constantly using their cellular telephones…As people do so, they are constantly connecting to cell sites [towers], and those connections are recorded by their cellular service providers….Using a cellular telephone is akin to using a tracking device and can function as a substitute for 24/7 surveillance without police having to confront the limits of their resources.”

 – Excerpt from a decision on February 18 by the highest state court in Massachusetts, the Supreme Judicial Court, declaring in the case of Commonwealth v. Augustine that cellphone users have a “reasonable expectation of privacy” in the data that identifies the locations where they have made or received calls on their devices. Thus, it ruled that police must have strong reason to believe that this data will provide links to crimes, and must get a search warrant to obtain the data.


The Founders who wrote guarantees of privacy into the Fourth Amendment used expansive language that would allow the zones of privacy to change and even expand with changes in the techniques of police investigations.  And with each new wave of technology, courts have to decide their potential for invasions of privacy.

The Supreme Court and lower federal and state courts are just beginning to analyze the impact on Fourth Amendment rights of digital age devices – especially, the ubiquitous cellphone.  Before summer, the Supreme Court will have something to say about police authority to examine the actual messages and images contained in cellphones that they take from individuals at the time of arrest.

Perhaps next after that, for the Supreme Court, will be the issue of police use of cellphone tower information to track the movements of users.  Lower courts, though, are already beginning to confront that question, and they are reaching conflicting rulings.

Whenever a cellphone user makes or receives a call, the nearest cellphone tower operated by the service provider will record data about the location.  With rapidly expanding use of cellphones, providers have had to install more towers, each covering less area, so the location data that they generate is even more accurate.  If police have access to that data, from multiple towers, they can essentially recreate the travels of the device’s user.

An illustration of that came in the Massachusetts case that the state Supreme Judicial Court has just decided.  Based on the state constitution’s guarantee of privacy that closely parallels that of the Fourth Amendment, the state court ruled that cellphone users have a “reasonable expectation of privacy” in the location data that their cellphone use generates, because of what that can reveal about where they go and – given the precision of the data – might even reveal what they might do at different spots.

Investigating a murder in Boston, police obtained from a Sprint service provider all of the location data generated by a suspect’s cellphone over a two-week period around the time of the murder – a compilation that ran to 64 pages of very specific location data.   For example, one lengthy call made on the suspect’s cellphone showed that the user went from Sullivan Square in Charlestown to the Haymarket area in Boston, to a transit station in Dorchester, and to the suspect’s home in Dorchester.

Police, however, had not obtained a warrant to get that kind of information, and, the state court decided, the state constitution required that they obtain a warrant because of the user’s right to privacy in that data.

The court made clear that the duration and the volume of the location information were factors it took into account, and it suggested that police would not need a warrant if, say, they only obtained tracking data for perhaps six hours or less.

Other lower courts, federal and state, that have reached opposite conclusions have ruled that the tracking data is simply a part of the business files of the service provider and, as such, cellphone users have no expectation that the data will remain private and not be turned over to police.

That alternative view basically traces back to Supreme Court rulings that came out well before the digital age and certainly before the enormous expansion in the use of cellphones.   The Supreme Court said in those decisions that customers voluntarily turn over the records of their banking activities to the banks (U.S. v. Miller, in 1976), and of their telephone use to the telephone company (Smith v. Maryland, in 1979), and such voluntary actions relinquish any claim to privacy that they might want to claim.

It should be noted that the federal government, in its defense of the massive telephone data surveillance carried on by the National Security Agency in terrorism investigations, relies very heavily upon the Smith v. Maryland ruling.  And the secret federal court that authorizes that broad surveillance program also has relied upon that precedent.

It is now abundantly clear that different courts are looking at these privacy questions in deeply conflicting ways, and that very likely will lead, sooner rather than later, to one of these cases reaching the Supreme Court.  The Massachusetts ruling would not be a candidate, because the Supreme Court will not second-guess a state court’s interpretation of its own state constitution.  But that ruling clearly adds to the perception that the privacy interests at stake are not going to be clarified in an ultimate way until the Supreme Court does so.

Lyle Denniston is the National Constitution Center’s adviser on constitutional literacy. He has reported on the Supreme Court for 55 years, currently covering it for SCOTUSblog, an online clearinghouse of information about the Supreme Court’s work.

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