SAFEGUARD YOUR EVERY EXIT: You will receive a doorbell and three receivers, open area range door sensor chime ensures you will never miss a visitor in every door/window, even if you are a few rooms away or on another floor. Note: The battery level will affect the signal receiving range of the doorbell, it is recommended to change every 12 months. 60 MELODIES & 5 VOLUME: Wireless doorbell features 58 chimes and 5 level adjustable volume(0 dB to 110 dB) to meet your needs for different occasions. LED indicators are suitable for the elderly and hearing impaired. Memory function: Keep the previous setted melody and volume level after re-plugging it. DOOR CHIME SENSOR EXPANDABL: One door chime receiver can be paired with up to many door sensors. By adding new sensor, you can also pair with different ringtone, so that you can realize exactly which door/window is triggered. EASY TO INSTALL: Plug the door entry chime receiver into socket, tear off the tape behind door sensor chime then paste on the door. The wireless door chime has been matched before shipment. If you need to replace music or add a transmitter, please re-match.(Please contact the seller once you have product problems.) LIFETIME CUSTOMER SERVICE: wireless door chime can be used for business, home, apartment, classroom, office, basement and more. "