The SK-4 and SK-4E (SK-4/E) are four zone conventional fire alarm control panels (FACPs) that bring the latest in microprocessor technology to conventional fire controls. The SK-4 is a 120 VAC FACP and the SK-4E is a 240 VAC FACP. These FACPs provide reliable fire signaling protection for small- to medium-sized commercial, industrial, and institutional buildings. The four zone SK-4/E is a 24 VDC FACP that provides four Class B initiating device circuits and two Class B notification appliance circuits (NAC). The SK-4/E NAC protocol includes the ability to silence audible devices while strobes continue to flash, using only a single pair of wires. The SK-4/E is also compatible with conventional input devices such as two- and four-wire smoke detectors, pull. stations, waterflow devices, tamper switches and other normally-open contact devices.