Algorithms that can tell identical twins apart. Eyebrows and earlobes that give you away. A new generation of technologies is emerging that can identify you by your physiology. And unlike the old crop of biometric systems, you don't need to be right up close to the scanner in order to be identified. If they work as advertised, they may be able to identify you without you ever knowing you've been spotted.

Biometrics had a boom after 9/11. Gobs of government money poured into face and iris recognition systems; the Pentagon alone spent nearly $3 billion in five years, and the Defense Department was only one of many federal agencies funneling cash in the technologies. Civil libertarians feared the worst as face-spotters were turned on crowds of citizens in the hopes of catching a single crook.