Eye movements could be next PC password

Pretty much all current eye trackers use the same basic principle. They illuminate the eye using infrared LEDs, which makes the pupil appear very bright when recorded with a camera of decent quality. The recorded stream, at least 500 frames per second if you want to be able to track microsaccades, is processed yielding X/Y coordinates. Only the fact you need that framerate and a decent focussed image makes it not easy to implement. To give you an idea, the trackers I have used are all made of cameras that do not fit in a latptop, or in some cases are even bigger than a laptop, and then either a dedicated real-time PC to run the processing or a set of PCI cards with some DSPs on it. Not exactly the kind of stuff you can simply add to an existing laptop or desktop. Furthermore all this only works properly after some calibration, adjusting settings based on background lighting etc and when the eye being tracked does not move too much in 3D space. In other words getting two tracks that are alike not only depends on how a person looks at things.

Sounds like a Voight-Kampff test.