ECO SIP System Terminal Indoor 2 button, working with Lucky Tone SIP microphone, other SIP telephones and devices. Adopt high-speed industrial grade chip, Support quiet and noisy environment mode, press to answer or auto answer, hangup on site or remote. Built-in speaker for intercom, With audio output for external active speaker, can work stand alone without any main control unit, With Amplifier (SIP-TL2)