This bell is designed for use in high noise level areas. Weatherproof for outdoor and indoor use. Bell loud enough To be heard in the noisiest factory or over extended distances outdoors. Has adjustable loudness control. Great for those with a hearing impairment. This ringer works in conjunction with your present phone ringer or independently. Installation is simple. Use a 4 conductor extension cable (Not supplied) with a 4 contact modular plug at both ends. Full instructions included. Specifications: Sound pressure level: +-95 dB (Excitation 20 Hz., 60 Volt, RMS). Minimum operating voltage is 40 Volts RMS (20Hz) Ringer impedance: greater than 8,000 ohms At 20 Hz. FCC Listed REN 0.8 A. ME956