Top quality product. For window or door. Entry warning ideal for homes, apartments, mobile homes, offices, hotel rooms, garages and more. Very loud 95 dB alarm. When someone opens the door or window illegally (the relative position of the primary and secondary parts change), the alarm can give out a loud alarm, warning the intruder to leave and reminding the owner. This magnetic sensor can detect the status of your door or window. It can prevent your children from sneaking around and provide security for children, homes, garages, mailboxes and businesses. You can easily install and use. Press the on/off switch to turn on/off the power, then insert 2 AAA batteries (no battery in the box). Peel off the sticker pad on the back of the door alarm sensor, and stick the door handle alarm on the target place. Super environmental friendliness and stability. Package contents: 4 magnetic sensors, 4 magnetic sticks.