12v powered alarm

Discussion in 'The Projects Forum' started by satchmolips, Jan 30, 2011.

  1. satchmolips

    Thread Starter New Member

    Jan 30, 2011
    Newby and not an electronics guy!
    I want to set up a simple alarm, 12v car battery with a car horn in the circuit. (I can manage that bit!). Challenge is I want this to operate when a circuit is broken. Basically I want to set up a trip wire that pulls apart some 7 or 15 amp wire that then sets the horn off. Preferably just connections made by twisting wire together to make contact, but would consider switch. Beyonde me so any helpful suggestions gratefully received.

  2. wayneh


    Sep 9, 2010
    I think you'll want to separate the mechanics of a trip-wire from the electronics by means of a limit switch. That's a switch with a lever and a spring in it, that will make (or break) a circuit when the lever is held in. Pulling the trip wire might be set then to remove an obstruction from the lever, allowing it to flip and complete the circuit.

    Limit switches are everywhere, such as anytime there is a door-closing sensor. You can probably find one without heading to the store.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    The cheapest can be done with a spring-closing clothespin. You push two thumbtacks in the inner parts of the jaws so the come in contact when closed. The wires may be soldered to the pin part.

    The trip is a bit of stuff plastic tied to the trip line, which can be invisible fishing monofilament. The plastic is placed so the clothespin clamps it, but the plastic holds the thumbtacks part.