The Extech CO30 displays carbon monoxide (CO) concentration, air temperature, and relative humidity. It features a programmable audible alarm with a high decibel beeper which sounds when CO concentration rises to unsafe levels. The 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. Complete with universal AC adaptor (including US, EU, UK, and AU plugs), and four AAA batteries.