Transcript for Supreme Court rules that police generally need a warrant to access cell phone data

Hello everyone I'm Terry Moran when ABC news in Washington has been a major decision in the Supreme Court today on privacy in the digital age of have to do. With what's called. Cell site location information records those are the records held by phone companies. From cell towers wherever you go with your cell phone you're always paying a cell tower. And up phone companies keep those records. The government has not needed a search warrant. To get those records from the phone companies and this case. Came from a man named Timothy carpenter he was suspected of being the mastermind of a series of armed robberies in Michigan and Ohio. And the federal government got the records. Dating back several months of where mr. carpenter was in when he was there and they could then use that as evidence to convict him of those armed robberies they did on appeal. Carpenter and his lawyer said the government should have to have a search court for getting information that delves that deeply. Into the private lives of Americans and today in a surprising ruling Chief Justice John Roberts joining the liberals on the court in a five to four decision. Said yes the government needs a search warrant in this digital age. To get the phone records of where you have been in when you've been there. From the phone companies this he says is a fact of life in the modern age that we are always carrying cellphones all the time. And that we have a reasonable expectation of privacy that we are essentially as he puts it being tail constantly. He's at if there was not. Fourth Amendment protection. From the government just tailing you through your cell phone wherever you go in whenever you go there. Essentially the only people could escape such surveillance tireless relentless surveillance he said are people the few people who don't have cellphones. In dissent justice Anthony Kennedy and justice Samuel Alito joined by justice Clarence Thomas. What they said was that this is something the government has been doing it can get your phone records from the phone coming about who you've called without a search warrant. Because you. By subscribing to it phone service you don't have that reasonable expectation of privacy but the bottom line here is the Supreme Court led by Chief Justice John Roberts. Has guaranteed a zone of privacy in the digital age saying that those records that phone companies keep. About where you're going every time you paying a cell phone tower that government can't get those. Without a search warrant demonstrating that they have probable cause to assume that you've committed a crime and can convince a neutral magistrate a judge. That they want to get those records and should happen so big case out of the Supreme Court today. I'm Terry Moran for ABC news alive keep watching.

This transcript has been automatically generated and may not be 100% accurate.