2PCS battery-free automatic wireless doorbell, long-lasting power saving, stable signal All digital FM technology, never string code simple design, elegant, chic style ultra-low power design, long-lasting use of power saving 150M long-distance remote control, signal stability 28ringtonestochoosefromand3-stepvolumecontrol(25~110dB) room bell volume Four adjustable outdoor unit does not require battery designed to last up25 years easy to installtion 1.Self-powered outdoor unit, no battery, moreenvironmentally friendly 2. The outdoor unit waterproof design, pay attention: is the PCB plating waterproof membrane, dont shell, PCB board bubble water does not affect the use Effectively solves problems that can beused normally in rainy days and can also be used in highly humid environments 3. The slim design of the outdoor unit can effectively prevent the outdoor unit from beingmaliciously picked 4.The indoor and outdoor units are made of ABS material (power supply pin is PC fireproof material), and the surface is enamel-printed. It is elegant and chic but also can effectively prevent the shell from being affected by the beauty after a slight cost-effective 5.Eye-catching backlight flashes when someone pushed the doorbell.particularly suitable for the elder,deaf and pregnant women