The Aiphone LEF-5 Open Voice selective-call master intercom with door-release button works with any combination of up to five Aiphone LAF and LEF Series master intercoms or LA, LE, and LS Series door and sub-master intercoms (sold separately) to enable audio communication with a visitor at a door and with other rooms within the building. Each intercom in the system must be connected to an Aiphone RY-PA relay (sold separately), which can connect an electric strike (sold separately) for door access control as well as connect devices such as CCTV cameras and lights (sold separately). Five buttons with LED indicators allow the master intercom to direct a call and communicate with the desired door or sub-master intercom.