The Breath Alcohol Detector is for rapid detection of the presence of alcohol in exhaled breath and provides relative Blood Alcohol Concentration (BAC) at 0.05%. The test is based on a chromogenic reaction. Alcohol, if present in the exhaled breath, reacts with the chemically coated crystals and produces a colour change. This colour change is proportional to the concentration of alcohol in the breath, which is an approximation of relative Blood Alcohol Concentration (BAC).
And im not putting my blesings on drink driving and i dont know how accurate it is.