The Extech CO30 is a CO Monitor which displays Carbon Monoxide (CO) concentration, Air Temperature, and Relative Humidity. The Extech CO30 features a programmable audible alarm with a high decibel beeper, sounds when CO concentration rises to unsafe levels. Unit can be wall mounted or used on a desktop close to areas of concern. Other features include a visible bright tri-colored (green, yellow, red) LED alarm indicator, a "ZERO" re-calibration function, manual temperature and relative humidity compensation (adjustable), CO calibration function in fresh air, and a low battery indicator.