Carbon Monoxide (CO) is a poisonous gas that you cannot smell or see. When a smoker inhales smoke from a cigarette, CO is absorbed into their blood through their lungs. CO is dangerous because it binds to haemoglobin in red blood cells about 200 times as readily as oxygen, depriving the body of the vital oxygen it needs to live. The device shows the amount of Carbon Monoxide in a smoker's breath (ppmCO), which is a measure of blood carboxyhaemoglobin (%COHb). It acts as an indicator as to the possible level of some 4,000 toxic substances in cigarette smoke, 60 of which cause cancer. Parts per million. In this case, one part CO in one million parts of air (breath).

Experience has shown that the best guidelines are:

0-6ppm: non-smoker

7-10ppm: danger zone (possible low-frequency smoking)

11-15ppm: smoker

16-25ppm: frequent smoker

26-35ppm: addicted smoker

36-50ppm: heavily addicted smoker

51+ppm: dangerously addicted smoker

Clinical research has shown that an optimum period of 20 seconds breath hold is required to get the best correlation with COHb. A 15 second breath hold gives almost the same correlation.

A disposable mouthpiece is used for each person taking the test. They are designed to be single-use only. These mouthpieces usually fit into a device connected to the CO monitor itself. These sampling systems contain one-way valves which stop people sucking air back from the monitors. A test takes only a few seconds. You may want to allow for a couple of minutes to include instruction, breath hold, and a confirmatory test if necessary.