Breath Alcohol Concentration (BrAC) and Blood Alcohol Concentration (BAC)
There are two ways of measuring alcohol concentrations. In some countries, alcohol limits are determined by the breath alcohol concentration, BrAC (not to be confused with blood alcohol concentration). However, most "in field" tests are done with a BrAC method even if the law is based on BAC levels. This is due to the fact that BrAC is relatively fast and easy to measure without inconvenience, and almost as accurate as BAC. The BrAC test will indicate if a BAC test is needed, and the BAC test can consequently be done at the police station or hospital, for example.
In many countries, our sensors would not be accepted in a court of law due to the fact that they are based on the BrAC method, but they could be used in workplaces and by law enforcement officers.
The IR spectrum of ethanol C₂H₅OH.
The broadest peak in the IR spectrum of ethanol comes from O-H stretches, similar to O-H bonds in water. This absorption at about 2.9 µm. Other strong stretching modes are C-H at 3.3 µm and C-O at 9.5 µm.
References:
http://en.wikipedia.org/wiki/Blood_alcohol_content
http://en.wikipedia.org/wiki/Breathalyzer
http://webbook.nist.gov/cgi/cbook.cgi?ID=C64175&Type=IR-SPEC&Index=2