There is a built-in super-direction back-electret electret head. When the microphone is working, there is a red light ring on the gooseneck (other representatives will know that the microphone is turned on) and there is an LED indicator with the same function on the front of the base. Each system can be connected to 60 representative units, which are divided into three-way serial connection, each unit is 20 units, plus extension unit can be connected to 180 representatives.