Are you thinking of biometric fingerprint sensor?
There is software called Upek Biometric Sensor software for Windows 7. If your fingerprint does not work then it displays password dialog.
I used this successfully on Win 7 since beta and it worked (reasonably) good.
You may want to visit www.upek.com or you can alternatively search for Upek biometric software using your favourite search engine.
Asus has face recognition that works only if I keep logging in from the same room (not working at all if I keep switching rooms, working from different locations etc)...
(Upek is a third party solution - I believe there are generic MS drivers in Win 7 that I have not tested...yet)
- Edited by dr.dissector Thursday, February 14, 2013 9:35 AM