A US federal appeals court has ruled that mobile phones can be searched to obtain their numbers without a warrant. Abel Flores-Lopez, who was recently sentenced to prison in a drug case, had appealed his conviction, saying that police had acted illegally when they searched his cellphone for its number. However, the Court of Appeals for the Seventh Circuit upheld the case, saying that even if searching a phone required a warrant — a question that is far from settled in most places — searching simply for its number is so "minimally invasive" that police don't need to obtain one. Since the phone was readily available when the police stopped the suspect, "if police are entitled to open a pocket diary to copy the owner's address, they should be entitled to turn on a cellphone to learn its number."

Continuing the diary comparison, however, the court stressed that not all cellphone searches are necessarily permissible. Just as police may not be justified in reading all the way through an obviously personal diary without good reason, the "vast body of personal data" in a phone may not be fair game for a search. And in the case of mobile phones or computers, the possibility for intrusion is even greater than in a diary. An app called iCam that lets the user monitor their house through a distant webcam, the ruling noted, could quickly turn a cellphone search into a house search.

The court declined to elaborate on where to draw the line between a reasonable search and an invasion of privacy. However, it said that such a decision might be influenced both by how invasive the search is and whether it's justified by an urgent need to preserve evidence or a legitimate safety concern — such as if the police suspect the phone is a disguised weapon like a stun gun. But those issues, according to the court, are "questions for another day."