The United States Court of Appeals for the Sixth Circuit in Cincinnati rejected that claim, finding that “although the content of personal communications is private, the information necessary to get those communications from point A to point B is not.” Therefore, the defendants had no privacy interest in the information held by the carriers about their location and the constitutional probable cause requirement did not apply.

The Carpenter case raises a fundamental question about how far the privacy protection in the Fourth Amendment, which by its terms applies to “persons, houses, papers and effects,” should reach in protecting data generated by a person’s electronic devices. Chief Justice John G. Roberts Jr. wrote in Riley v. California, a 2014 decision, that cellphones are now “such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy.”

In Riley, the court found that a warrantless search of an arrestee’s cellphone was unconstitutional, explaining that what distinguishes the device from other items that might be found on a person that the police could look at “is their immense storage capacity.” But rummaging through the contents of a phone or computer is not necessarily the same as getting site information that is broadcast to the carrier, especially when a person may enable it by using an app like Find My Phone.

In a 2012 case, United States v. Jones, the Supreme Court found that the use of a GPS tracker attached to a car was a search governed by the Fourth Amendment. Justice Sonia Sotomayor explained in a concurring opinion that the privacy interests in a person’s specific location required investigators to get a warrant because gathering that information “enables the government to ascertain, more or less at will, their political and religious beliefs, sexual habits, and so on.”

In the Carpenter case, the justices will have to weigh whether cell site data is different from a GPS tracker because learning where a person is within about a one-mile radius may not be a sufficient invasion of privacy to come within the Fourth Amendment. Nor does obtaining the location of a cellphone reveal the content of any communication, only that a call was made, so the protection afforded by the Riley decision may not apply.

Another case involving the Stored Communications Act that may come before the justices concerns the territorial reach of a warrant authorizing investigators to obtain emails held by Microsoft. The United States Court of Appeals for the Second Circuit in Manhattan, in Microsoft v. United States, found that the warrant did not apply to emails stored on a server in Dublin because there was no indication in the statute that Congress intended to authorize a search outside the United States.

The Justice Department filed a petition with the Supreme Court on June 22 asking for a review of that decision, arguing that it was “wrong, inconsistent with this court’s framework for analysis of extraterritoriality issues, and highly detrimental to criminal law enforcement.” Those requests are often granted because the justices rely on the solicitor general’s office to identify cases that have significant law enforcement implications.