2PCS Battery-Free Automatic Wireless Doorbell - Long-lasting power, stable signal. All digital FM technology, no code interference. Simple design, elegant, chic style. Ultra-low power consumption, long-lasting use. 150M long-distance remote control, stable signal. 28 ringtones to choose from and 3-level volume control (25~110dB). Adjustable indoor unit volume with four levels. Outdoor unit requires no battery. Designed to last up to 25 years. Easy to install. 1. Self-powered outdoor unit, no battery needed, more environmentally friendly. 2. Outdoor unit's waterproof design: PCB plating is waterproof membrane, do not peel. PCB board bubble water does not affect use! Effectively solves problems that can be used normally in rainy days and can also be used in very humid environments. 3. Outdoor unit's slim design effectively prevents the outdoor unit from being intentionally picked up. 4. Indoor and outdoor units are made of ABS material (power is PC fireproof material), and the surface is enamel printed. It is elegant and chic but can also effectively prevent the shell from being affected by beauty after a slight cost-effective. 5. Eye-catching backlight flashes when someone presses the doorbell. Especially suitable for the elderly, deaf, and pregnant women.