One of the fascinating Fourth Amendment questions that courts have recently divided on is how the “search incident to arrest” exception applies to the search of a cell phone.

This discussion is closely related to the border search question - when someone is arrested can the police read all their email on their smart phone "incident to arrest." I think the answer is no but coming up with a workable rule that allows the kinds of searches that should be allowed will be very difficult.

The Volokh Conspiracy » Georgia Court of Appeals — Including “Feddie” — Weighs In On Search Incident to Arrest for Cell Phones