Breathalyzers – How Do They Work?  

Breathalyzers analyze your blood alcohol content (BAC) through your breath. The BAC indicates if you are legally drunk or impaired, which is why breathalyzers are most commonly used by police officers to determine if drivers are driving under the influence or while intoxicated. A BAC of .08 is the legal limit at which a driver is considered legally drunk and will be arrested immediately; a BAC of .04 can be considered driving while impaired and often carries a lesser charge. Breathalyzers are the most convenient way to test for BAC levels. Here’s how they work.

Alcohol absorption

Alcohol begins being absorbed into the body as soon as it enters the mouth. The mucus membranes of the mouth, throat, and esophagus all absorb alcohol before it reaches the stomach. From there the alcohol enters the bloodstream and shortly reaches the lungs, where the alveoli (the parts of your lungs that take in oxygen and expel carbon dioxide) start to give off alcohol as well as CO2. Because of this rapid absorption, the alcohol given off by the lungs is directly proportional to the amount of alcohol in the bloodstream, which makes Breathalyzers give very accurate BAC readings.

Air-to-blood ratio

The breathalyzer is programmed with an air-to-blood ratio that automatically converts the presence of alcohol in the breath to the amount of alcohol that is in the blood. This ratio is 2100:1, meaning that 2100 mL of air equates to 1mL of blood, and the amount of alcohol in these two amounts is therefore identical. So a BAC of .08 means there are actually .08 mL of alcohol per mL of blood, or .08 grams of alcohol. And since a breathalyzer measures exactly 2100 mL of the air you blow in to it, you can be sure that the reading will be accurate.