[axman6]

You're looking at the process backwards. Just because latches exist does not mean that, at the time the patent was filed, it was obvious to use a latch analog to unlock a digital device. A person skilled in the art would NOT be lead directly to that solution, but one which is already know: a pin, password, fingerprint, keycard, heck even facial or voice recognition. The test is not "did latches already exist" but "is it obvious to use them in the method claimed, as the time of application", and I would strongly argue that it is not, without some evidence to support the contrary.

I say this as someone who has worked as a patent examiner and understand the law (not the US law exactly, but they're quite similar world wide).