If you had asked a legal scholar yesterday, they would have told you the Fourth Amendment was in trouble. Historically, it's been the main force protecting your privacy — it's the reason police need a warrant to search your home, and can't arrest you without a charge — but a lot of those rights haven't survived the shift to digital media. There are a lot of laws about searching a person’s home or office, but as files have moved to cloud accounts and mobile devices, many of those rights haven’t held true. Bit by bit, the right to privacy has been slipping away.

For privacy advocates, it's the best news in a long time

But today, everything changed. In a historic 9–0 decision on Riley v. California, the Supreme Court offered one of the most stirring defenses of the Fourth Amendment in years. The immediate issue was cellphone searches: police now clearly, unambiguously need a warrant to search your cellphone. The contents of your phone, like the contents of your house and your car, are now protected from warrantless search. But the ruling could also have implications far beyond your phone, for everything from cell interception devices all the way up to the NSA. The highest court in the land is now firmly on the side of a strong Fourth Amendment, and for privacy advocates, it’s the best news in a long time.

"The Founders did not fight a revolution to gain the right to government agency protocols."

In particular, the court's language could apply directly to future challenges against NSA collection of phone records. The decision goes on at length about how revealing large amounts of data can be, at one point observing that "the sum of an individual’s private life can be reconstructed through a thousand photographs labeled with dates, locations, and descriptions" — indicating that such data should only be accessible with a warrant. While the court was clear that today’s ruling only applies to specific "searches" (rather than aggregates or bulk collection), the same logic could be used to attack many of the legal bedrocks of NSA surveillance, including the much-cited third-party doctrine. Taking on privacy-preserving protocols designed to allow for searches, Chief Justice Roberts noted: "the Founders did not fight a revolution to gain the right to government agency protocols." If the NSA wants to claim it’s not violating the Fourth Amendment because of minimization protocols, that could turn out to be a very inconvenient quote.

"All signs point to the Supreme Court eventually rejecting [the third-party doctrine]."

Already, privacy advocates are taking the language as a sign of new support from the Supreme Court. Trevor Timm of the Freedom of the Press Foundation thinks the language shows that the Supreme Court may be ready to reevaluate some antiquated precedents. "The government has been relying on one case from the mid-1970s, Smith v. Maryland, that allowed the police to get just the phone numbers dialed of one suspect for three days, and have warped it into allowing the NSA to get metadata on everyone essentially forever," Timm says. "The 11th Circuit rejected that interpretation two weeks ago [in US v. Davis], and with today's decision, all signs point to the Supreme Court eventually rejecting that interpretation as well."

As an intelligence agency, the NSA works by a very different set of laws than regular law enforcement, so it’s unlikely that the ruling will affect the NSA directly. The ruling gives new privacy rights to digital media, but it’s not at all clear that the Supreme Court will want to apply those rights to bulk collection under FISA warrants.Still, even if the court doesn’t go on to address NSA collection, the language in today’s ruling could still affect other digital privacy issues beyond requiring a warrant to search a suspect’s phone. The Electronic Frontier Foundation's’ Hanni Fakhoury says that law enforcement use of Stingray devices, which fake cell-tower signals to collect phone data, could be subject to legal challenge under the same reasoning as Riley v. California.

"Like finding a key in a suspect's pocket and arguing that it allowed law enforcement to unlock and search a house."

The ruling also hints at new privacy protections for files in the cloud. It’s a huge quantity of data, from emails in Gmail to photos in Dropbox, which had previously been seen as something of a legal no-man’s land. Discussing the search of cloud data through a suspect's phone, the justices wrote, "such a search would be like finding a key in a suspect's pocket and arguing that it allowed law enforcement to unlock and search a house." That language gives the cloud a lot of legal protection and, as Orin Kerr puts it at The Volokh Conspiracy, it "only makes sense as a concern if there is Fourth Amendment protection in stored contents in the cloud, too."

It’s still early to say how far the Supreme Court will press the logic and how eagerly lower courts will follow its lead. Lawyers at EFF and the ACLU are celebrating tonight, but they will face a lot of opposition extending this ruling to other areas. Like any legal victory, it could be reigned in or carved out by future rulings. But for the first time in decades, the Supreme Court is recognizing that your data is as important as the objects in your home — and as a result, many advocates are beginning to treat the Supreme Court as an ally rather than an enemy. For a single day, that’s quite a turnaround.