EASY INSTALLATION – no wiring needed; battery-operated (requires 1x9V battery,not included),push the turn on button in the back of the door stop alarm into working status;place it under the door,the gap bewteen the bottom of the door and the floor should be 10mm(0.38 in) to 35mm(1.35 in),it can not slide on tile or smooth hardwood door when door opens,smooth floor can try to use H-type sensitivity,vibration-sensing alarm.,DOOR STOPPER SECURITY ALARM – the door stopper alarm in "on" status,when door pressure is applied,the door alarm will be triggered while make extremely loud 120db alarm,helps wake/alert homeowner or renter, helps deter intruder and possibly notifies neighbors,security protection.,NON-SKID DOOR STOPPER – the door stopper alarm in "off" status,it can be used as common damping rubber base door wedge,hold door in open position,no any loud alarm sound.,3 SENSITIVITY LEVELS – Low - Medium - High,with an adjustable sensitivity switch on the side;H level is the most sensitive level that vibration will trigger an alarm;please note when the alarm sound gradually becomes smaller,it means to replace the new battery.,PORTABLE DOOR STOPPER ALARM – package include one door alarm,each weight about 120g;easy to carry;alarm loud 120db to protect you;great for travel;ideal for bedrooms, hotels, apartments, dorm rooms, front doors, etc;peace of mind when traveling or working alone.