"If [..] a different person standing in front of the computer screen, the PC will not operate."
Careful there. In professional or even private environments, someone coming over to see what's on your screen for whatever reason is very common. If the scanner can't cope with two hearts in the same vicinity, things will get ugly quickly. Not to mention that sometimes the helpdesk guy just has to sit in the chair and do stuff. I hope the scanner will be up to that as well.
And if it can, then the burglar doesn't care about the scanner - he can just tie the victim up, drag him to the PC and then do whatever he wants.
This tech may be fine to control access to physical areas, but I'm not convinced PC access is the right area to apply it.