On: Lockitron: Keyless entry using your phone

[mikesun]

uh, where'd you get 24? how about 10 X 9 X 8 X 7 = 5040 combinations.

[mappu → mikesun]

>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.

[rogerbinns → mikesun]

Because from fingerprints and similar gunk on the pad you can tell which 4 digits were used.