Extech co100 desktop air quality meter extech co100 the extech co100 air quality meter checks for carbon dioxide co sub 2 sub concentrations using a maintenance free non dispersive infrared ndir co sub 2 sub sensor this neat desktop unit displays indoor air quality in ppm with good 0 to 800ppm normal 800 to 1200ppm and poor gt 1200ppm indication if required poor air quality will trigger a visible and audible co sub 2 sub warning alarm complete with universal ac adaptor e