A great, easy to use, easy to carry alarm perfect for business trips or hotel stays. The Door Guard Alarm works on vibration and by simply hanging it on a door knob, it will detect any sort of attempted entry. The built-in 98db alarm will scream for 20 to 30 seconds then reset itself. A sensitivity adjustment screw takes care of false alarms with an easy turn of the screwdriver. The Door Guard Alarm is also an LED flashlight, which is really useful in dark motel doorways, parking garages and just about any emergency that requires additional lighting. The unit is very easy to use and has a price you can't beat. Requires 2 AAA batteries (not included). 4” × 2”