The way people walk can be used for ID and health checks

LISTEN carefully to the footsteps in the family home, especially if it has wooden floors unmuffled by carpets, and you can probably work out who it is that is walking about. The features most commonly used to identify people are faces, voices, finger prints and retinal scans. But their "behavioural biometrics", such as the way they walk, are also giveaways. Researchers have, for several years, used video cameras and computers to analyse people's gaits, and are now quite good at it. But translating such knowledge into a practical identification system can be tricky--especially if that system is supposed to be covert.