idea for new periperial device

Sorry, this might be percived as an offtopic, but I didn't find better
place for posting.

Recently on my mind come an idea for the device that would trace the
user eye orientation towards the screen. When we have such an information in
computer we can do a lots of useful things e.g.:
- auto strafing (sorry I'm not english native ) in fps,
changing the cocpit view in flight simulations etc.
- auto scrolling in document readers, editors, browsers
- others (which currently I dont know :-) ) .

Hmm I think that device would be better from the virtual helmet, since the
v.h. has the limited motion range, the traditional monitor is less tiresome
for eyes, and lcd or crt generates better image than the v.h and that device
would be easier to implement for the pcs (portability etc.) than v.h. Does
such device exist ? What do you think of that idea ?