Adinnieken on 23 May 2013
it measures the pulsations in the neck. How accurately, I don't know. However, they appear to be taking two different measurements in order to determine the pulse.
The method for doing this is describe in a recent patent awarded to Microsoft as well.
Basically an image is taken, then the differentiation of that image against the previous one is determined. This is then done about 100 times per second.
