The Fourth Amendment's protection against unreasonable searches prohibits police from searching your cellphone without a warrant. In 2014, the U.S. Supreme Court ruled that this is true even for someone who has been arrested.
But can police allowed to get location data from your cellphone provider?
A pending case before the Supreme Court, Carpenter v. United States, raises this important question.
What are the facts of the case?
The Carpenter case concerns a series of armed robberies of Radio Shack stores in Michigan and Ohio, starting in Detroit in 2010. The property taken included laundry-bags filled with smartphones.
In 2011, police made four arrests in the case. One of the people arrested confessed and implicated Timothy Carpenter as one of the organizers of the robberies.
Most of the suspects pleaded guilty, but Carpenter did not. At trial, the prosecution introduced evidence of Carpenter's location information, obtained from his wireless provider without a warrant.
This location information matched up with the location of the robberies and helped prosecutors get a conviction against Carpenter.
Why didn't police get a warrant?
The police chose to use a law called the federal Stored Communications Act rather than getting a warrant.
They probably did this because requesting records from wireless providers under the Stored Communications Act was easier than getting a warrant. Getting a warrant requires a showing of probable cause to a judge that the required information contains evidence of a crime.
A warrant therefore places tends to place more limits on what police can do than requests made under a statute like the Stored Communications Act.
How is the case likely to turn out?
Commentators are watching the Carpenter case closely. Some are calling it the most important case of the 21st century for electronic privacy issues.
In two recent decisions, the Supreme Court has expressed concern about letting law enforcement have easy access to too much digital data. The Court has already ruled that a search warrant is generally required to search a cellphone's contents. In another case, the Court also restricted the use of GPS devices by police to monitor the locations of suspects.
The lower courts in Carpenter, however, did uphold the police's use of location data obtained from the wireless provider without a warrant. And when the case received oral argument before the Supreme Court in November, it was unclear how the justices are leaning.