Battery-free Style Wireless (656Ft) Waterproof and Wide Temperature Doorbell Door Chime(1 Transmitter +2 Reveivers) Open to the transmission distance of 200 meters;20 years of product life Transmitter from power, do not use batteries and other external power supply;waterproof design, easy for outdoor use 16 polyphonic ring tones, built-in amplifier, voice quality is better support learning mode, the user can set their own pairing mode (one to one, one to many) No wiring, easy to install,Applicable for villas, offices, yard,school,hospital