In an era of 5-4 decisions, Wednesday’s unanimous ruling by the U.S. Supreme Court was as heartening as it was unexpected. Clearly drawing a line of privacy regarding electronic data, the court put warrantless cellphone searches off-limits to police. It was a critical ruling at what is still the dawn of the digital age.

The ruling grew out of criminal cases from Massachusetts and California, in which lower courts came to different conclusions. But, despite some musings during arguments this spring, the justices were firm and unequivocal. Writing for the court, Chief Justice John G. Roberts Jr. noted that the term cellphone is an inaccurate description of what is, in fact, a miniature computer capable of making telephone calls.

Noting that the American Revolution was driven, in part, by anger over “general warrants,” that “allowed British officers to rummage through homes in an unrestrained search for evidence of criminal activity,” Roberts observed that modern technology allows people to carry such information in their hands. That technological fact, he wrote, “does not make the information any less worthy of the protection for which the founders fought.”

And that, exactly, is the point. The Fourth Amendment protects against “unreasonable searches and seizures” and it doesn’t matter if that means British officers searching a house without a warrant or police trawling at will through the electronic data on a cellphone. Both are unreasonable invasions of privacy.

What is more, the remedy for police seeking information on a crime is hardly onerous. If they have reason to suspect the phone contains relevant evidence, they can get a warrant. In the meantime, the personal data on cellphones – everything from calls and text messages to travel history and medical information – is safe from random searches. Roberts also noted that if police are in an authentic “now or never” circumstance, a warrantless search may be allowed by an “exigent cirumstances” section of Fourth Amendment law. This is an eminently correct and reasonable ruling that united liberal and conservative justices.

Justice Samuel A. Alito, filing a concurring opinion, made an important observation about the crucial – and largely unfulfilled – roles of Congress and state legislatures. Noting that technology allows the gathering of masses of information and that many Americans willingly make that information public, Alito wrote that “… it would be very unfortunate if privacy protection in the 21st century were left primarily to the federal courts using the blunt instrument of the Fourth Amendment.”

He’s right. Congress and the states also need to wrestle with these issues. But they should do so understanding that, with this broad court decision, a clear line has been drawn: Americans’ digital information is private. The laws they may draw up need to protect and support that fundamental Americans concept.