when a reed switch comes close to a magnet both parts attract causing them to come together and continue the flow of electricity. Attach the magnet with tape to the inner part of the door so it can swing.
attach the final two wires so that the circuit is complete now when the bar magnet comes close to the reed switch it will buzz. To make a disarmer put a piece of tape under the magnet and reed switch (see pic). Now you can put a piece of thick paper between the magnet and reed switch from the outside and be able to walk in without it going of. You may have to adjust it to your desire. Thanks for viewing my instructable!