1. Super loud 120 dB alarm. When someone opens the door or window illegally (the relative position of the primary and secondary parts changes), the alarm can issue a strong alarm, warning the intruder to leave and remind the owner2. Magnetic sensor switch detects your door or window.Easy stick installation and operation, press on/off switch to power on/off then insert 2 AAA battery (battery do not contain in the box),tear the double-sided adhesive on the backpack, paste the door knob alarm on your target position.3. The alarm gives out clear and loud sound when an intruder breaks in. Freely switch control. Emit super loud sound once the burglar gets in. Suitable for window or door warning.4. Super environmental suitability and stability.5. Easily mounted by adhesive. Type to window or door. Ideal entry warning for homes,apartments,mobile homes,offices,hotel rooms,garages,and more.