This from Chris Wilson at NYT this morning:
A team of Dutch and Italian researchers has found that the way you move your phone to your ear while answering a call is as distinct as a fingerprint. You take it up at a speed and angle that’s almost impossible for others to replicate. Which makes it a more reliable password than anything you’d come up with yourself. (The most common iPhone password is “1234.”) Down the line, simple movements, like the way you shift in your chair, might also replace passwords on your computer. It could also be the master key to the seven million passwords you set up all over the Internet but keep forgetting.