The Operating Interface Units (Models FCM2018-U3 and FCM2035-U3) function as the operator interfaces and central microprocessors for the Cerberus PRO fire- alarm control panels (Models FC922 and FC924); the Cerberus PRO Intelligent Voice Communication [IVC] systems (Models FV924 and FV924), as well as the Fire Terminal (Model FT924). The Model FCM2018-U3 and Model FCM2035-U3 operating units provide multi-use capability for each end-user to efficiently ‘Acknowledge’ events; to quickly control the notification-appliance circuits (NACs) of the corresponding fire alarm control panel (FACP), and to permit a manual reset of the respective system. Detailed information about the nature and location of the events can also be displayed, via a 5.1 cm. x 12.1 cm. backlit LCD screen. An audible will sound in any instance where there is an ‘unacknowledged’ event taking place on either Model FCM2018-U3 or Model FCM2035-U3 operating unit.