Retinal scans are out, iris scans are in. If I remember correctly, beyond the age of 5 the iris banding pattern remains the same. Retinal scans get tripped up by things like pregnancy and other health issues. I'd never use it for a password though, as there are commercial products that perform iris scans at a distance of several meters on non cooperative subjects. The first thing I thought of when I saw the product, sort of a virtual turnstile, was Snowcrash and the surreptitious collection of biometric information for eventual sale on the black market.