Virtually every state in the union, including New York, defines intoxication as the percentage of alcohol in the blood stream, commonly called the blood alcohol content (BAC). In New York, a BAC in excess of 0.08% means that the person is intoxicated and may be guilty of drunk driving. If a police officer suspects that a driver may be intoxicated, the driver may be asked to submit to a breathalyzer test. The breathalyzer measures the person’s BAC by sampling the person’s breath. How does such a test reveal the level of alcohol in the person’s blood stream.

When a person drinks, alcohol molecules pass through the stomach and enter the blood stream. Some of the alcohol molecules in the blood stream enter the alveoli in the lungs and are passed out of the body when a person exhales. The more alcohol a person has consumed, the more alcohol molecules will be expelled during exhalation. The rate at which the body passes alcohol molecules into the lungs is roughly the same for every person, and the breathalyzer uses this fact to determine a person’s BAC.

The breath test requires the suspect to exhale into a tube. The tube passes the breath into a small chamber. The air in the sample chamber is scanned with infrared radiation. The rate at which alcohol molecules absorb this radiation is a well-established constant. Thus, the breathalyzer’s circuitry is able to translate the reading of IR absorption into the percentage of alcohol in the blood stream. A small LED screen provides the BAC, and the police officer can then determine if the driver’s BAC level exceeds the legal limit.

A breathalyzer test cannot be defeated. The science has improved to the point where courts uniformly accept the readings unless other factors are present. A person who fails a breathalyzer test will usually be charged with Driving While Intoxicated (and any other crimes detected by the police). Anyone who has failed a breathalyzer test may wish to consult a lawyer who handles drunk driving cases. Such a consultation can provide a helpful analysis of the law and facts that govern the case and an estimate of the likelihood of obtaining a favorable plea agreement or an outright acquittal.

Source: Forbes, How Does A Breathalyzer Test Work?