Mengshen 3-Pack Safety Wedge Door Stop Alarm Stopper Blocking Travel Home Security Alert 120db (pack of 3) MS-M68 3 Sensitivity Levels - Low - Medium - High, with an adjustable sensitivity switch on the side. Also works as a wedge to prevent door from opening when powered off. No installation required. Requires one 9 volt battery. Portable and easy way to add piece of mind when traveling or working alone. Extra loud alarm. 120 decibel alarm sounds when pressure is applied to door stop.