PDE Tech ZDSA-120 Door Stop Alarm Door Stop Alarm is perfect for dorm rooms&#44; apartments&#44; cabins&#44; and hotel rooms. A simple&#44; effective way to safeguard your home&#44; or even your personal space on the road&#33; Just place doorstop in front of your door If an intruder attempts to break in&#44; they"ll trigger a 120dB siren. Uses one 9-volt battery &#40;not included&#41;.