[kandu]

What kind of radiation does it use for sensing (infrared, ultrasound, visible light, ...)?

[Bjartr]

Looks like light of some kind

http://www.youtube.com/watch?v=LY3Ya__6BHw#t=183s

[thighmaster]

it uses IR illumination from 3 rather large IR leds. A problem with this approach like all other IR approaches is that it's quite subject to IR interference from itself (unwanted reflections), sunlight, halogen lights, etc... not much you can do about it.