This product is a smart doorbell which is unlike the traditional wireless doorbell. It is simple & easy to operate, has stable transmission signal, fit for apartment, villas, home, hospital and many other places.This product is according to the rules of the frequencies using of our country. It won’t produce harmful electromagnetic interference.Please carefully read the use manual to correctly grasp the installation, operation methods.Features1. simple design, elegant, chic style;2. ultra-low-power design, energy saving and sustainable use3. 300 m long distance remote control, stable signal;4. 36 polyphonic ring tones for optional;5. Adjustable indoor ring volume. http://www.doorbellalarm.com/