We're all familiar with the 4th Amendment to the US Constitution, right? The one that states that you're secure from "unreasonable searches and seizures?" Right, well, we all know from our TV-watching that the key word there is "unreasonable." Turns out that the most-common of police encounters, the traffic stop, could potentially open you up to having your smartphone searched.
Basically, if the police officer arrests you for real, he or she can then search your person -- including your iPhone -- without a warrant:
Adam Gershowitz, an assistant professor at the South Texas College of Law, raises an interesting point about the iPhone and similarly tricked-out mobile devices: If the police stop you and find some legal cause to arrest you, they are probably free, under judicial interpretations of the Fourth Amendment, to search the device. - Machinist
That's a scary thought, actually, because it's one thing to search a car, but to search an iPhone is tantamount to searching your entire life. Think about it: email, browsing history, received phone calls, all of it.
Of course, there's always the chance that when this gets tested for real in court, that court will set a precedent that will overturn this. As of right now, though, the ability to do that search is the best interpretation of current law.
What do to? Apparently if you just set a screen-lock password, a warrant is required. I'm not just saying this as a PSA to criminals, either -- setting the screen lock is a good idea all around. If your iPhone gets stolen, welcome to the special circle of hell reserved for those whose identity has been stolen. Not. Fun. (and no, I'm not just talking about iPhones, either.)
So that screen lock is a hassle, but it might just be worth it, no?