Your home and your cellphone are practically the same. So the U.S. Supreme Court ruled unanimously last week in a broad and inspired opinion, written by Chief Justice John Roberts, fitting founding principles into the digital age. The court recalled the “general warrants,” which “allowed British officers to rummage through homes in an unrestrained search for evidence.” The practice contributed to a revolution and led to the privacy protections erected then and that endure today.

Warrantless searches long have been permitted in connection with arrests. They are viewed as necessary to protect police officers and to prevent the destruction of evidence. What the chief justice did so effectively was explain why these justifications do not apply to cellphones and, more telling, how a cellphone differs from a purse or wallet or address book.

A police officer can assess quickly whether a cellphone poses a risk, for instance, a sharp blade somehow hidden. What the chief justice stressed is that the data hardly endanger officers, and that the possibility of suspects destroying evidence is remote. He argued that the current exception, allowing searches under urgent or emergency circumstances provides sufficient leeway.

What makes a cellphone like your home? The sheer volume of the data they typically contain. The chief justice accurately described the devices as a “pervasive and insistent part of daily life,” amounting for people to “a digital record of nearly every aspect of their lives — from the mundane to the intimate.” He noted the typical smartphone user has installed 33 apps, their use a “revealing montage” of a life.

A smartphone can track practically every movement, and search histories point to interests. The chief justice concluded that these devices are not just phones. They are “cameras, video players, Rolodexes, calendars, tape recorders, libraries, diaries, albums, televisions, maps or newspapers” — or what amounts to the place where you live. Thus, they deserve the same protection, which now logically extends to laptops, and tablets. Law enforcement authorities must get a search warrant to look inside.

Will all of this make police work more difficult? The chief justice acknowledged that it likely would, though he added that new technology also accelerates gaining warrants. Most important, he emphasized that privacy must carry the day, even if it comes at a cost. Similar thinking applied two years ago when a unanimous court barred authorities from attaching a GPS device to a suspect’s car without a warrant.

Worth adding is that law enforcement officials often prefer clarity as much as anything. They adjusted well to the Miranda requirements. And that points to what is heartening about the court’s ruling, the laying down of clear boundaries, applying honored principles in a new era.