The trouble is they're working with a very limited UI. Lockout after X attempts (as another comment mentioned) is a terrible idea, because that makes it a simp

The trouble is they're working with a very limited UI. Lockout after X attempts (as another comment mentioned) is a terrible idea, because that makes it a simple DoS mechanism. But forcing a delay, for example, is tricky -- how do you notify the user that they're in a delay period? Or when the delay period has ended and they can try again after a mis-key? There don't even seem to be LEDs to work with.... If they keys light up, that's easier (e.g., flash the key lights for 10 seconds if they enter a wrong code before they can start over).