On: Lockitron: Keyless entry using your phone

[mappu]

>I've actually encountered keypads where the order didn't actually matter

If the order really doesn't matter, then that counts combinations twice (1234, 1243..). There are 10000 possible 4-digit codes, 5040 permutations, and actually 210 combinations.

[rogerbinns → mappu]

You haven't taken into account that by looking at the keypad you can tell which digits are actually used.