At only 2.5" long this economical door alarm or window alarm inconspicuously protects your home from intruders. Uses a magnetic sensor to detect the opening of a protected door or window. A 90 dB alarm will alert you to an attempted entry and scare off potential intruders. The owner may open the window or door, without setting off the alarm by switching the on/off switch to the off position. May also be used within the home to alert parents to children opening a gun or medicine cabinet or used to protect exterior doors, particularly those hard to protect sliding glass doors. Commercial uses include showcases and cash registers. Uses three 1.5 volt button style batteries. Includes batteries and double sided tape for mounting.