The Bogen Model SCR25A Call-In Module is an annunciator latching control bank designed for use with room selector panels in Bogen Multi-Graphic® systems. The SCR25A provides 25 silicon controlled rectifiers (SCR) and permits the use of momentary switches without SCRs.The silicon controlled rectifiers provide annunciator latching, keeping the appropriate LED annunciator lamp on the room selector panel illuminated until the call is acknowledged.