Premium Transmitter: Works with CR2032 Lithium battery to provide 3 years of battery life. Waterproof construction (waterproof index = IP55), operating temperature between -20C and 60C. This doorbell is resistant to strong winds and heavy rain. Long wireless range: 400m long transmission distance, covering the whole house without interfering with other devices. 52 beautiful melodies: A generous selection of 52 melodic ringtones lets you choose the sound you like. 5 adjustable volume, the maximum volume is 115dB, suitable for the elderly and hearing impaired. Memory function: This doorbell can memorize volume and ringtone settings. Therefore, in the event of a power outage, once power is restored, the doorbell will automatically restore the last saved settings. Easy to Install: The doorbell can be easily and quickly mounted to the wall, using dowels and screws, or the supplied rubber pads. This doorbell system can be expanded with 2 transmitters and multiple additional receivers for extended coverage.