https://www.theverge.com/2018/6/22/17424740/supreme-court-carpenter-decision-privacy

In a major decision on privacy in the digital age, the Supreme Court ruled 5-4 today that police must generally obtain a warrant to seize cellphone tower location records.

The case, Carpenter v. United States, centered on whether there was a reasonable expectation of privacy when location records were held by a third party, like a phone carrier, and was closely watched for its Fourth Amendment implications.