[Easy to install]:Just plug the doorbell receiver into any standard outlet and tear the double- sided adhesive tape which on the back of door sensor( or screw mounted) and stick them to the door or window is fine,please take the insulating paper away before using the sensor [24/7 Lifeguard for Your Family]: This child/ home door sensor alerts when burglar opens door and helps deter break-ins(entry alert chime activates when magnetic sensor separates) [Adjustable Volume Control & 52 Chimes Options]:5 levels of adjustable volume from 0-110 dB. Offer 52 elegant music from the traditional"Ding Dong" to various well know chimes. Memory function: Keep the previous setted tune after re-plugging it [Wide Working Range]:This wireless door open chime for home is up to 400 ft in open area, magnetic door sensor will automatically trigger the receiver when the magnetic strip is separated and the receiver will alerts immediately whenever the door or window is opened [Mini Contact Sensor]: Magnetic door sensor (Size:3. 0x1. 0x0. 60ininch),magnetic strip (Size:1. 7*0. 6*0. 4 inches). They are small size and can be installed or placed at any indoor position to provide you with a door entry chime/alert system.