(High Sound Quality and Compact Installation Call Amplifier) A4 size does not take up much space to install. Wall mountable Features a screwless terminal block that allows you to easily connect speaker lines. (Factory Off Setting) Microphone, mute line volume when calling on paging. It can be switched between two outputs of SP1 and SP2. Built-in emergency shut-off circuit. Phone paging control (Input only, no power control)