I suppose you could say there's just one 'but' about this biometric authentication method—and it's your posterior . Turns out your keister—or, more specifically, the way you sit—can be used to identify you. One team of researchers has created a prototype of a car seat that can tell who's sitting in it. It's not only great for making sure that only you (or, presumably, your family) can start your car, but also potentially handy for ensuring that your seat, mirrors, and other preferences are automatically adjusted for you.