his Electronic Lock circuit is not only simple but it is also very good. It can easily be configured to provide either momentary or continuous output. Key sequences of up to 9 digits are possible. You can pre-enter part of the combination and then have someone else enter the last few digits at a later time allowing for one-time access. This circuit has good debounce but there are some REALLY crappy switches out there so please look for types with spring or snap contacts. For better security or for a mad-scientist look you might use unlabelled pushbuttons arranged in some unusual shape.