How do breathalyzers work?

Alcohol is absorbed into your bloodstream primarily through the stomach and intestines.  The rate of absorption depends on many factors, including your weight, whether or not there is food in your stomach and your body’s metabolic rate.  Deep within your lungs there are tiny blood capillaries that interface with the air.  This is where the alcohol in your bloodstream is evaporated into your exhaled breath.  The alcohol breathalyzer then determines the content of alcohol in your breath.

Any type of alcohol breathalyzer depends on an alcohol gas sensor to measure the content of alcohol in your breath.  Most professional breathalyzers use a fuel cell alcohol sensor, while most consumer breathalyzer use a less expensive semiconductor sensor. The content of alcohol in your breath is assumed to be directly proportional to that in your blood.

Professional quality alcohol breathalyzers contain a flow sensor that requires that you blow for a minimum amount of time at a minimum flow rate to assure that you expel enough air out of your lungs to get to the “deep-lung” air, where the most accurate alcohol breathalyzer reading can be obtained.  The better quality consumer breathalyzers also contain a flow sensor so that they can obtain a deep-lung sample. All BreathKey models use a flow sensor.

With any alcohol breathalyzer you must wait about 20 minutes after your last alcoholic drink before testing.  This is because any alcohol that is left in your mouth after your last drink is at a very high concentration when compared to the alcohol that is in your exhaled breath.  Alcohol in your mouth will result in erroneous blood alcohol readings, so you must wait for the mouth alcohol to dissipate before testing.  If you choose not to wait at least twenty minutes you may receive a breathalyzer false positive.  This false positive result can occur whether you use an expensive professional breathalyzer or an inexpensive consumer breathalyzer.