The proverbial ink wasn’t even dry from yesterday’s recap of Edward Snowden’s chilling account of the extent to which the government can literally take control of any cellular phone, when the Supreme Court of the United States (SCOTUS) published its landmark opinion in Riley v. California, which requires police to get a warrant before searching a cellular phone. Despite the ubiquitousness of cellular phones for over a decade, not to mention smartphones and the iPhone, during more than half that time, until yesterday, SCOTUS had not pronounced any sort of constitutional threshold governing the search of cellular devices. In 38 short pages, that is all history. But what does this landmark decision really mean to most of Americans?

Even before yesterday, police couldn’t (lawfully) snatch the cell phone of every random person walking down the street. But before yesterday, the police could search the phone of any person they arrested, for any reason, or no reason at all. Whatever evidence the police recovered during that search could then be used to charge the individual with additional crimes. For example, if you were arrested because of having unpaid parking tickets (yes, that’s really possible in some states, like New Jersey), and the police found text messages relating to drugs, gambling, or anything else, you could then be charged with those other crimes, even though they aren’t at all related to the “crime” for which you were arrested in the first place. That is pretty much what happened to David Riley.

Riley was stopped by police, for having expired registration tags. During the stop, they discovered his license was also suspended. When impounding Riley’s car, police discovered two illegal handguns, for which Riley was placed under arrest. When they took Riley into custody, police took the smartphone that was in his pocket, and after looking through the phone, found text messages evidencing Riley’s gang involvement, and a picture of Riley in front of a car that had been involved in a recent shooting incident. Ultimately, Riley was charged with that prior shooting, and with sentencing enhancements for gang affiliation. He was convicted of all the charges, and sentenced to 15 years to life in California prison.

Modern smartphones were unheard of ten years ago, [but they] are now such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy.

The Court threw out Riley’s conviction because it found that it was unreasonable for the officers to search Riley’s cell phone under the attendant circumstances. The Court examined the history of the “search incident to arrest” exception to the warrant requirement, noting the reasons it was created, the most important of which was for officer safety—to ensure that a suspect didn’t have weapons close at hand, which could be used to harm the arresting officer(s). “These cases require us to decide how the search incident to arrest doctrine applies to modern cell phones, which are now such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy.” The Court also noted that the “digital data stored on a cell phone cannot itself be used as a weapon to harm an arresting officer or to effectuate the arrestee’s escape.”

On that reasoning, all nine justices of the U.S. Supreme Court unanimously agreed that absent some other exigent circumstances, police cannot search a cell phone without first getting a warrant. And so the same court that all but repealed the Fourth Amendment sua sponte has come back and redelivered a substantial portion of those privacy rights back to Americans. “We cannot deny that our decision today will have an impact on the ability of law enforcement to combat crime. Cell phones have become important tools in facilitating coordination and communication among members of criminal enterprises, and can provide valuable incriminating information about dangerous criminals. Privacy comes at a cost.”

You can read or download the full opinion below.