If the police want to track you through your cellphone's location history, should they have to get a warrant?
Requiring that law enforcement officers get a warrant is meant to protect people from unduly intrusive searches and seizures. The Fourth Amendment to the U.S. Constitution promises that people will be "secure in their persons, houses, papers, and effects, against unreasonable searches and seizures."
Although the case law is very complex, the courts have generally read the Fourth Amendment to mean that law enforcement needs a warrant, or a specific exception to the warrant requirement, before most searches of suspects' persons and property.
Obtaining a warrant requires the officer to show probable cause to believe that the suspect has committed, is committing or is about to commit a crime. Probable cause is essentially defined as objective facts and knowledge from reasonably trustworthy sources that are sufficient to convince a person of reasonable caution. Judges are not to issue warrants unless they agree that probable cause exists.
Since a 1979 Supreme Court case, however, the courts have generally ruled that the Fourth Amendment's prohibition of unreasonable searches and seizures does not apply to property or information held by third parties. This includes business records, and telephone company records were ruled to be business records.
This business records rule has allowed officers to obtain telephone company records (and many other kinds of records) merely by issuing a subpoena. Subpoenas have no probable cause requirement.
In the case recently before the Supreme Court, law enforcement obtained a robbery defendant's cellphone location data. The data demonstrated that he had been in the area during each of a string of robberies in Michigan and Ohio. The police got this data without a warrant, and the lower courts found that the business records rule justified that.
The Supreme Court responded by changing the business records rule to exclude cellphone location data. Chief Justice John Roberts, writing for the 5-4 majority, said that there have been "seismic shifts in digital technology" and found that cellphone location data is "detailed, encyclopedic and effortlessly compiled."
"When the government tracks the location of a cell phone," he wrote, "it achieves near perfect surveillance, as if it had attached an ankle monitor to the phone's user."
In other words, unlike other types of business records, cellphone location data impinges so directly upon a person's privacy that it triggers the protection of the Fourth Amendment.
Going forward, the ruling says, law enforcement officers are expected to obtain a warrant before seeking cellphone location data except in emergency situations.
Justices Kennedy, Alito, Thomas and Gorsuch dissented from the decision.