A desktop/wall-mount monitor that simultaneously displays carbon monoxide (0-999 ppm), relative humidity (10-90% RH), temperature (0-50C), and the time/date on one LCD screen. It offers a user-adjustable CO alarm limit, max-hold function, and a built-in clock/calendar, and runs on 4 AAA batteries or the optional R9450-ADP AC adapter. Suited to continuous CO monitoring in offices, garages, and warehouses.