The Magnetic Door Switch from Bellman & Symfon is an accessory specially designed to work with a Visit Transmitter or Receiver, as part of the Visit Smart Home System. Typically, just mount the Magnetic Switch on the door or window frame and connect it to the Telephone Transmitter or Baby Cry Transmitter. When the magnets are separated by opening a door or window, it will activate the transmitter to send out a radio signal to the receiver wirelessly that alerts you with audible sounds, bright flashing lights, or strong vibrations (depending on the receiver). This way, you will be notified immediately when someone is trying to open a door or window. It is a great alerting accessory that helps people with hearing loss, hard of hearing, and deaf to keep track of the comings and goings within your house.