Background Music Input, Optional Alert Tone and Repeated Alert Tone, Transmit And Receive Volume Controls, Screw Terminal Connections; ACCESS: 600 ohm Two-Way Page Port on Selected Telephone Systems, Electronic Key System C.O. Line Key, PBX Loop Start Trunk Port, Or Dedicated Single Line Phone Set; Specifications: Input Impedance: 600 ohm; Music Source Impedance: 8 ohm; Music Input Level: 1 to 3 W; Power Requirements: -24 Vdc, 300 mA; Shipping Weight: 1.5 lbs (0.86 kg) Dimensions: 7.25" H x 4.5" W x 2.0" D (18.42 cm x 11.43 cm x 5.08 cm)