*Door/window Entry Alarms*,Senses door movement Disturbing sound 1 year battery life ~Easy stick,*Cost $4usd each* or *$10USD for 3*,How it works,A door and window alarm sensor works by using a sensor and a magnet. The sensor is… More placed on or inside the door or window frame. The magnet is placed on or inside the door or window itself. When the door or window is opened, the magnet will separatee from the sensor, causing it to activate.

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