The Fourth Amendment requires, as a general rule, that police officers obtain a warrant based on probable cause before searching “persons, houses, papers, and effects.” This was a central concern of the framers of the Constitution and Bill of Rights, who knew well the danger of “general warrants” that allowed government authorities to enter a home and rummage around looking for incriminating evidence.

There are a few narrow exceptions to the warrant requirement. For example, when police officers lawfully arrest someone, they may search his or her body and immediate surroundings and seize any belongings to ensure officer safety or the preservation of evidence. But mobile phones aren’t weapons and pose no physical threat, and any evidence on the phone can be preserved by using special devices to prevent remote deletion of the data.

The government nevertheless argues that mobile phones are no different from other personal items that may already be searched, like wallets, purses or address books. But the exception for searches incident to arrests was limited by the constraints on what a person could physically carry. Modern mobile phones have obliterated that rationale. Of the new iPhones, the smallest-capacity model can hold the equivalent of 16 pickup trucks of paper, thousands of photos or hours of videos.

In other words, permitting police officers to search a mobile phone, or any digital storage device, essentially gives them access to someone’s entire life; allowing them to do so without a warrant renders the Fourth Amendment’s guarantee against unreasonable searches and seizures meaningless. This is not a hypothetical concern. There are 12 million arrests in America each year, most for misdemeanors that can be as minor as jaywalking. The majority don’t end in a conviction, and yet if the government wins this case, any one of them could result in the warrantless search of the person’s phone.

The Supreme Court has recognized the need to adapt to new technologies, as when it ruled that the government attaching a GPS tracking device to a private car was a Fourth Amendment search. For better or worse, mobile phones have become repositories of our daily lives, and will become only more powerful over time. As a rule, the police should have to get a warrant to search them.