The Magnetic Door Alarm is a compact, attractive and uses magnetic affinity to initiate its 110 dB Siren. The base of the magnetic door alarm is attached to a door or window frame and the actuator is attached to the window or door. The magnetic door alarm will be activated when a door or window is opened. The magnetic door alarm works great with any door or window particularly those hard to protect sliding glass doors. The magnetic door lock comes with three lithium cell batteries.