Physen Wireless Door/Window Sensor Chime,1 Magnetic Door Sensor,Operating at 260-feet Range,4 Volume Levels with 52 Melodies Chimes for Home/Office/Stores Take care of you family: Alerts when burglar opens door and helps deter break-ins(entry alert chime activates when magnetic sensor separates) Working Range:The range of wireless receiver up to 260ft in open area, magnetic door sensor will automatically trigger the receiver when the magnetic stripe is separated and the receiver will alerts immediately whenever the door or windows is opened Contact Sensor: big door magnetic(Size:1.77*0.95*0.35inch),small door magnetic(Size:0.9*0.35*0.31inch).They are small size and can be installed or placed at any indoor position to provide you with a door entry chime/alert system Powered by CR1632 battery(Battery Included) You can add more sensors as you need and just follow the "pairing operation" to make sensor pair with the receiver before using it is ok.