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.

The court ruled 5-4

“Given the unique nature of cell phone location records, the fact that the information is held by a third party does not by itself overcome the user’s claim to Fourth Amendment protection,” the majority opinion, written by Chief Justice John Roberts, reads. Location information obtained by police should generally be considered a search, and law enforcement should have to reach a probable cause standard to obtain those records, the court ruled.

The court said in its majority opinion that the decision was a narrow one, and that it would not extend its decision to matters involving “conventional” surveillance tools like cameras, nor to data collection in national security contexts. But the ruling still noted the “seismic shifts” in technology that have changed our conceptions of privacy. “Sprint Corporation and its competitors are not your typical witnesses,” the majority opinion reads. “Unlike the nosy neighbor who keeps an eye on comings and goings, they are ever alert, and their memory is nearly infallible.”

“ Sprint Corporation and its competitors are not your typical witnesses.”

The court rejected the government’s argument that there was not a reasonable expectation of privacy when phone location records were held by a third party. The decision notes those records are enormously sensitive, and that the case “is about a detailed chronicle of a person’s physical presence compiled every day, every moment, over several years.”

High-profile tech companies, including Apple, Google, and Facebook, wrote in support of Fourth Amendment privacy protections in a filing to the court last year. Timothy Carpenter, who was convicted of robbery charges after police tracked his phone records, was represented by the ACLU in the case.

“This is a groundbreaking victory for Americans’ privacy rights in the digital age,” ACLU attorney Nathan Freed Wessler said in a statement. “The Supreme Court has given privacy law an update that it has badly needed for many years, finally bringing it in line with the realities of modern life.”