The DOOR GUARD ALARM is a versatile vibration alarm that can be used in any number of applications. There is no installation required. Just hang the unit on any door knob and it will detect any vibration. When vibration is detected, a ear splitting 98 decibel alarm is sounded for 20 to 30 seconds. After that period of time, the alarm will reset and rearm. Easily adjustable sensitivity allows you to set the alarm to your preference. Ideal for travelers, feel secure in any hotel or motel. Can also be used as a small lamp if needed. This unit requires two AA batteries (not included)