Door Knocker Bell

If you have an old house, it’s nice to have only a door knocker and no doorbell, since ‘back then’ no-one had a doorbell and it destroys the illusion of authenticity. Although a door knocker makes quite a racket, if you happen to be in the garden, the attic or the cellar it might not be enough. The circuit shown here solves this problem by acting as a sort of ‘electronic extension’ for the door knocker.