How does it work?
It’s a two part thing: Hardware and software.
The “typical” hardware looks like a long bar positioned along (or built into) the bottom edge of the computer screen. This bar has three sets of near-infrared lights (left end, center and right end) and an optical sensor that are directed in the general direction of the user’s eyes. The tracker and computer will evaluate where the reflection of the light is on the eyeball, in comparison to the location of the pupil, then use the collected data to tell in which direction the user is looking.
There is another type of eye tracker which looks more like a traditional camera