Get it here: https://www.intercomsonline.com/master-to-sub-system This simple wired intercom system provides two-way communication between two points. It is very simple to use. To call the substation, press the OFF and TALK buttons together to produce a tone on the substation. Or you can simply press the TALK button to speak without sending a tone. Release the TALK button to listen. Press the Off button to put the unit into standby. If this is not done the master cannot be called, but the area around the substation will be continuously monitored. To call the master from the substation, simply press the CALL button. It rings the master as long as the button is pressed. When the master answers, the substation can talk handsfree without pressing a button. The voice volume on the master is adjustable by a control on the side of the master station. The master station and substation can either be surface or wall mounted, or desk mounted. They wall mount on a single-gang box or ring. This is a kit that set includes a desk or wall mount master station, a desk or wall mount substation, and an AC transformer to power the system. This intercom requires 2 conductor shielded cable between the door intercom and monitor. #IntercomSystem #WiredIntercom