A 4-digit electric combination lock locks this vault which is similar to an ATM's or a mobile's PIN security: the passcode ranges from 0000 to 9999 (which numbers are needed to be entered in the appropriate order) and the system allows three attempts to enter the right code. Once the right combination is entered, the vault opens and the system automatically resets itself to its initial state. If someone fails all three attempts to get the code right, then ... well, see for yourself. The best thing about this construction is that it is very easy to change the lock's combination once you are inside: there is no need to rewire anything, only a few levers are needed to be flipped.

The map can be downloaded from here (updated to 1.8):
http://www.mediafire.com/download/u2lap017nvv7266

The passcode for the lock is set to 0000, but feel free to set and try out other combinations too. Let me know please if you experience any malfunction (there shouldn't be any as long as the buttons are not punched too quickly). I started building it in Minecraft Beta 1.8.1 and finished it after Minecraft was already upgraded to Minecraft 1.1 so it should be compatible with any versions after those.