Visidon - facial recognition - locker
I have had this app for a few days now and thought I'd recommend it, Its great.
You can use it as a lock screen or to lock individual apps, its fast and accurate.
It scans your face and only unlocks if it finds a match, very clever.
The only down side I have found is that it isn't brilliant in very low light conditions, obviously.
There is a free version but some functions only work in the full version.
Samsung Galaxy S2, Nexus 7 16GB