In what is considered a major victory for privacy rights, the U.S. Supreme Court has ruled that law enforcement must generally obtain a warrant before accessing cellphone location data. This data, which Chief Justice John Roberts called "detailed, encyclopedic and effortlessly compiled," can be so revealing about the user's movement that it amounts to surveillance.
The ruling follows up on a 2014 case in which the high court ruled unanimously that a warrant is required before law enforcement can search the contents of a suspect's cellphone, even when that person has been arrested.
In the case before the court, the defendant was suspected of taking part in a series of robberies in Ohio and Michigan. Using a court order that required a lesser standard of suspicion than a warrant, the police obtained cellphone location data records spanning 127 days. Using that data, they were able to place the defendant near the location of each robbery at the time that they happened.
The Fourth Amendment to the U.S. Constitution prohibits "unreasonable" searches and seizures by government agents, including police. Warrants are meant to protect people from unreasonable government intrusion into their privacy. Judges are not to issue warrants unless they independently verify that there is probable cause to believe a crime has been committed, is in progress, or is about to be committed.
Although the law in this area is quite complex, courts generally require warrants before a person's private property can be searched or seized, unless a specific exception applies.
The robbery defendant challenged the disclosure and use of the cellphone location data, claiming a warrant should have been used to obtain it. The lower courts ruled that no warrant was required because the data was simply a business record owned by the cellphone carrier. Therefore, they concluded, the defendant had no realistic expectation of privacy in those records.
There is an exception to the warrant requirement for third-party business records, but it was created in the context of a 1986 case. That case involved a single land-line phone and telephone company records that amounted to no more than a list of telephone calls made to or from that phone.
In this case, the court recognized that there have been "seismic shifts in digital technology," such as cellphones that can carry virtually all of a person's private information.
"When the government tracks the location of a cell phone," wrote Chief Justice Roberts, "it achieves near perfect surveillance, as if it had attached an ankle monitor to the phone's user."
The court made clear that it was not overruling the entire third-party business records exception. Other business records, including bank records, can still be obtained without a warrant. Moreover, it clarified that even cellphone location data could be obtained without a warrant in an emergency, as it declined to address this issue, as well as real-time cell phone location data and "tower dumps."