Testo 0632 3173 317 3 gas meter testo 0632 3173 p carbon monoxide is a particularly dangerous gas it is colourless odourless and above all lethal the 317 3 co meter from testo measures the concentration of carbon monoxide in the surrounding air and presents the readings on an easy to read display p p this meter has both a visual and an audible alarm which are triggered when a threshold is crossed the thresholds can be adjusted individually p p what s in the box br co monitor br