Daqq writes –
The Concealed codelock (CC for short) is a design of mine, which can be used in a similar fashion as a safe lock… The rotation sensor used here is just a simple 10k potentiometer. The concealability in this is that you can use a double potentiometer. One part of the potentiometer will be used for the lock and the other one for something else, such as a amplifier, or any other normal home apliance that has a potentiometer for something.
The concealed codelock – Link.