Use someone *else's* face as your unlock.
Like Teddy Roosevelt.
And then put that picture as your login screen, so it'll log you in if you point at a mirror.
It'll still be a problem if Zombie Teddy Roosevelt steals your phone, but how likely is that...
So you now have a cell-phone that's only useful near mirrors.
And completely useless if you're a vampire.
Leopards don't change their spots.
They just become snow leopards.
...Likewise I bought Final Fantasy 10 for $20 and have been playing it for ten years.
Not really very good at gaming, are you?
I think there's a world market for about five computers. -- attr. Thomas J. Watson (Chairman of the Board, IBM), 1943