This 110dB Mace alarm switches itself on as you approach and goes of 15 seconds after you leave the 20 foot scan radius. The Mace daylight sensor makes it perfect for indoor or outdoor use.  This small yet entirely effective device uses movement activated PIR (Passive Infrared) technology and will not use power during the daylight hours so you can count on it working for you when you need it.  Perfect for dorms, of campus housing and studying abroad.