The Supreme Court is one step closer to resolving a long-running civil liberties debate: do police need a warrant to search your cellphone? This morning, the court is hearing arguments on two cases, both of which involve evidence gathered from mobile phones after an arrest. They were contentious enough to reach the Supreme Court because of the quickly changing nature of phones, which have gone from a simple communication tool to a centralized hub for our daily lives. And the final decisions, expected early this summer, will determine how much weight these technological changes are given when interpreting the Fourth Amendment's proscription of unreasonable searches.

"Cellphones and other portable electronic devices are, in effect, our new homes."

The two cases, Riley v. California and United States v. Wurie, have spent years running through appeals courts. The first stems from a 2009 gang shooting. While separately investigating the case, police stopped David Leon Riley for expired registration tags and found guns and other "gang paraphernalia" in his car, leading to his arrest. By searching his cellphone, they found more evidence of affiliation, including contact names, photos, and videos. Riley was subsequently linked to the shooting, convicted of attempted murder, and sentenced to 15 years in prison. His counsel argued that this conviction relied on evidence, including the cellphone contents, that had been gathered in an invasive and illegal search. So far, this argument hasn't been successful.

The same can't be said for US v. Wurie. The case involves the 2007 arrest of Boston man Brima Wurie, who was arrested for buying crack cocaine. Later, police noticed that his confiscated flip phone was receiving calls from a number labeled "my house," and by opening the phone, they were able to find the number and link it to what turned out to be Wurie's address, which they confirmed partly by looking at the phone's wallpaper. A search turned up guns, ammunition, and more drugs, and Wurie was sentenced to over 20 years in prison. But an appeals court vacated the decision, saying that police weren't justified in looking through his phone. "The Court, more than thirty-five years ago, could not have envisioned a world in which the vast majority of arrestees would be carrying on their person an item containing not physical evidence but a vast store of intangible data," wrote Judge Norman Stahl. Without the threat of harm or destruction of evidence, phone searches could become "a convenient way for the police to obtain information related to a defendant's crime of arrest — or other, as yet undiscovered crimes — without having to secure a warrant."

The details of the cases differ, and they hinge partly on factors like how long the police waited after the arrest and what information they drew from the phone. But the Supreme Court's decision will also need to clarify whether a cellphone should be treated like a wallet or address book — as the police contend — or like a computer whose contents can be expansive and deeply personal. After an arrest, police are allowed to search items "immediately associated" with the person involved. As cellphones have become smarter, civil liberties advocates have tested how far that doctrine reaches, and that largely means defining what exactly a phone is.

"At the touch of a button a cellphone search becomes a house search."

A 1969 case established that arresting someone in their home didn't justify searching the entire house, although police could search the area within the person's immediate reach (to find, for example, a weapon.) In a supporting brief, the ACLU argued that these protections should be extended. "Cellphones and other portable electronic devices are, in effect, our new homes," reads the filing. "They can contain voluminous quantities of information about the most intimate details of our lives ... Especially for younger generations, the importance of the worlds of their portable electronic devices rivals the importance of their physical dwellings." In an unrelated 2012 ruling on cellphone searches, United States v. Flores-Lopez, Judge Richard Posner referred to the large stores of information that "even the dumbest of modern cellphones" contained. On more advanced phones, apps could grant police access to things like home security cameras. "At the touch of a button a cellphone search becomes a house search," he said.

But the actual history of phone search rulings is checkered and incomplete. Posner ultimately concluded that the court didn't need to clarify broad rules for cellphone searches, since the one in question only yielded the phone's own number. The Wurie and Riley decisions both involve more extensive searches, but judges came to opposite conclusions. A widely cited California case from 2011, People v. Diaz, found that police could search a confiscated phone for text messages even after the arrest was made. The nature of the object, the ruling said, didn't affect the right to search it after an arrest, and the simple cellphone in question didn't have features or storage capacity that might raise larger questions. It's possible that the Supreme Court will issue a limited ruling that still leaves these larger questions unanswered — and we'll still be debating what rules apply in special cases like border searches. But today's arguments will help it decide whether an increasingly connected and technologically mediated world deserves a new legal framework.