The RS-442 is a switch board designed for use with the N-8400RS 4-wire substation interface unit. It is equipped with 1 microphone input (with a microphone unit), 3 switch inputs for call buttons, and 1 speaker output, enabling you to make a switch panel suitable for applications. By assigning a different master station as a calling destination to each Call button, you can call one of them and make a conversation.