Seiko Epson is commercializing a tiny 0.2mm fingerprint sensor that will allow manufacturers to secure any kind of mobile device. The sensor reads fingerprints by detecting the miniscule electric current from your finger when you touch the device.
Possible applications are self-identifying credit cards, cellphones, and MP3 players. When a wrong fingerprint is entered, that item is disabled, so your credit cards won't be charged and your phones won't be used to make strange calls. Unless they take out your SIM and stick it in another phone, that is. Then you're screwed.