Arduino controlled secret knock detecting doorlock: The circuit is configured as per the diagram given. The Arduino is uploaded with the code given. The code is run. Knocks are performed by tapping against the piezo electric sensor. Default knock code is "Shave and a hair cut, two bits" (according to the rhythm in which we say it). All knock parameters like tolerance level and fade time can be modified within the code. Also possible to record new knock code and save.