This is an order sensitive combination lock with buttons. The circuit is super compact and secure. The combination lock has 6 buttons, but it is possible to make it bigger.

Each button has one RS NOR latch. When all the RS NOR latches are activated, the combination is correct, and the circuit sends a short pulse from the output. The pulse goes to a T flip-flop that controls the piston door.
If the wrong button is pressed, the circuit actomatically resets. This makes the lock very safe!