This is a simple "one-way on" alarm system for securing a door or window.I wanted an alarm that would keep going off if someone opened up my storage locker. Cheap alarms like this GE 45115 will go off when the door is opened, but are hard to mount on awkwardly-shaped doors. This object is in two parts -- a bottom part that holds the alarm unit, and a top part that sits loosely on top and holds a disk magnet. Use a piece of string to attach the top part to the door, and attach the bottom part anywhere else. When the door opens, the top part falls off and the alarm goes off until the top unit is put back in place. Demo video: https://www.youtube.com/watch?v=r47WJlzlMjQ