Carbon Monoxide Analyzer: Carbon Monoxide Monitor measures the ambient concentration of carbon monoxide (CO) in the environment and displays the measurement on the two line digital LCD screen. Besides the measurement, the maximum recorded CO value since the last reset is shown. An audible carbon monoxide alarm gives warning of CO levels. For viewing in poorly lit environments, the built-in backlight brightens the display. Model 450A includes soft carrying case with belt loop, wrist strap, and batteries.