? 58 MELODIES & 5 VOLUME: Wireless doorbell features 58 chimes and 5 levels adjustable volume(0 dB to 110 dB) to meet your needs for different occasions. LED indicators of the doorbell button are suitable for the elderly and hearing impaired. Remembers your last melody and volume level after a power outage; no need to reset to your previous settings. ✨ 150 M/600 FT OPEN AREA RANGE: Doorbell chime signal can easily cross through doors or walls, ensures you will never miss a visitor, even if you are a few rooms away or on another floor. Note: The battery level will affect the signal receiving range. It is recommended to change it once every 12 months. ? EXPANSION SYSTEM: Door/window door sensor chime will detect every entry and send alarm warning to the doorbell chime receiver to better protect your place. You will hear the door bell chime to remind you when someone opening your door/window or your pet coming home. Each door sensor or receiver can be expandable for business, home, apartment, classroom, office, basement and more. ? EASY TO INSTALL: Plug the door chime for business when entering 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 (Hold Receiver's music button over 3 seconds to 5 seconds, it will trigger clean pairing function).