Wednesday's unanimous decision by the US supreme court in Riley v California is a resounding victory for digital privacy. It's also a "no-duh" moment for American justice. Of course smartphones aren't the same as cigarette packs. No, there's nothing in the App Store that can be used to shoot a police officer. And, yeah, accessing hundreds of photos and text messages without a warrant is probably an invasion of privacy.

But the decision to rule warrantless cellphone searches unconstitutional is, overwhelmingly, a lot better for privacy advocates than expected. Chief Justice John Roberts, who wrote Wednesday's opinion, showed what could politely be described as a shaky grasp of technology during oral arguments in multiple cases this term. Many civil libertarians feared the worst: it was never clear that this court would know how to turn a wi-fi router on and off, let alone rule the right way on phone surveillance.

Roberts is, after all, a man who writes his opinions by hand; in 2010, he asked what the difference between e-mail and a pager was. Not that the rest of the bench is doing any better than your grandparents struggling to make conversation about the internet during Thanksgiving dinner – Riley came down minutes after the court ruled the Aereo streaming service to be illegal, a decision that might have devastating consequences for other cloud-based technologies.

Maybe the millennials who clerk for the supreme court don't understand web streaming, but they, like most of the country, understand that the 90% of the population with cellphones carry "a digital record of nearly every aspect of their lives – from the mundane to the intimate." And Roberts read his hand-writing on that from the bench, loud and clear.

The opinion in Riley acknowledges our present reality with what nearly passes for tech savvy: the ubiquity of cellphones ("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 huge and varied amount of data they can contain ("they hold for many Americans 'the privacies of life'"), and the existence – ! – of the cloud ("the data a user views on many modern cell phones may not in fact be stored on the device itself"). John Roberts even knows something about remotely wiping the contents of a device – though he's likely never used the Find My iPhone app.

The supreme court still has serious misunderstandings about technology – though, bizarrely, it may have worked out for the best: Roberts confuses encryption with "locking" a cellphone with a passphrase, a not-insignificant mistake that led him to conclude that police do not need the ability to immediately search a cellphone at the site of an arrest.

What does this mean for the future of digital privacy as it relates to your constitutional right to security from unreasonable search and seizure? Maybe not much. Riley and its companion case, United States v Wurie, are about a very specific exception to the Fourth Amendment. (It doesn't mean anything for border searches, or the bulk collection of data by the NSA.)

You see, "search incident to arrest" is one of the exceptions to the constitutional warrant requirement for search and seizure – meant largely to protect officers and preserve evidence. When a suspect is arrested, an officer is allowed to search him for weapons. This common-sense exception was eventually extended to include the search of "containers" like cigarette packets, but until Wednesday courts have been split on how to treat cellphones.

In Riley, one court found that the search of a smartphone was constitutional; in Wurie, a different court found that the search of a flip-phone was un-constitutional. Trapped between confusing precedents and their frequently limited understanding of technology, judges in the lower courts have sought to analogize cellphones to everything from purses and wallets to address books and photo albums. A smartphone, capable of carrying gigabytes of data and accessing all kinds of personal information in the cloud, is clearly different from those things – even if it contains digital versions of them all.

Now, at last, the supreme court has sent a loud and clear message that they get it: a lot of us wouldn't let a loved one look through our text messages, so why let a police officer? But still – it's a little tragic that "getting it" is cause for rejoicing.

On the other hand, maybe Riley is just the beginning. Hidden in a stray citation halfway through Wednesday's ruling, under a WebMD joke, Roberts quotes his colleague Sonia Sotomayor in the case of US v Jones, where she sketched out an alternate theory of the Fourth Amendment that could be huge for looming privacy cases. Indeed, earlier this month, the 11th Circuit Court of Appeals found that cellphone tower tracking data must be acquired with a warrant. Some commentators think that's a misinterpretation of the Fourth Amendment – and maybe it is, according to what the supreme court has said in the past. But technology is changing, and even this Luddite bench has noticed.

But I still wouldn't trust any of the justices to fix my wi-fi. Not any of the nine.