Carbon Monoxide Meter detects the presence of carbon monoxide (CO) and measures concentrations between 1-1000 parts per million (PPM). The Meter indicates the presence of CO by a reading on the LCD and a beeper tone. The beeper function much like clicking of a Geiger counter: Above 200 PPM, the beeper sounds continuously with the concentration of CO. From 35 PPM to 200 PPM, the beeper sounds discontinuously with the concentration of CO