We’ve had an older (and non-biometric) version of this for several years now — one with a numeric keypad instead of a fingerprint scanner. I saw it in action at an acquaintance’s house, and geek that I am, installed one on our own door soon thereafter. It’s quite useful, and if the batteries ever do wear out, you can always use a key.

(I happen to like the belt-and-suspenders approach, thank you… it’s like always keeping a backup, a lesson that I [like anyone who uses computers] learned the hard way a long time ago.)