[Dual Function]: Can be used as a door stop alarm and door stopper, Its high damping rubber bearing can prevent the door sliding and prevent the bad guys into. [3 Level of Sensitivities]: Hige-Midium- Low Sensitivities. Which depends on the distance door touch the door stop alarm. [Loud Alarm]: Very loud shrill that would definitely scare someone away with 120db alarm. Weight: 4.5 oz. [Powered by 9V Battery]: Powered by 9V battery, One piece can be used for a year under normal circumstances. (Note: Battery not include) [Easy to Use]: NO installation required, Simply place the alarm behind any door (home, hotel, etc).