Since his letter-box is outdoors and quite some way from the house, the author was looking for a simple means of knowing if the postman had been without having to go outside (contrary to popular belief, the weather isn’t always fine in the South of France). Circuits for this kind of ‘remote detection’ come up regularly, but always involve running cables between the letter- box and the detection circuit in the house. Seeking to avoid running any extra cables, the author had the idea of using the existing cables going to the doorbell, conveniently located adjacent to his letter-box. The letter-box has two doors: one on the street side for the postman, and one on the gar-den side for collecting the post. A micro switch is fitted to the street-side door, to light an indicator in the house showing that the postman has been. A second micro switch is fitted to the door on the garden side, to turn off the indicator once the post has been collected. The only ...