A musical electronic lock

A motorised gate is jolly useful, just so long as you don’t forget the remote control or the key. Normally, the control system for this type of gate makes provision to connect a push-button for opening or closing it without needing a remote control or key. This button must not be accessible from outside, whence the need for a more complex system. The code lock suggested here lets you control up to three such gates using push-buttons after entering a valid secret code.