Alcohol breathalyzers are made to determine the amount of alcohol a person has in their bloodstream, called the BAC or blood alcohol content. The BAC is an important number, because it determines whether a person is considered legally drunk while driving. This is called DWI, or driving while intoxicated; or simply DUI, driving under the influence. The two terms correspond to different BAC numbers which are determined by a breathalyzer used by police in the field if a person happens to get pulled over because he is driving suspiciously. This level can be confirmed by a blood test.
The breathalyzers work by measuring a breath or respiration made by the person under suspicion. Because of the way it is absorbed by the body, through the mucus membranes in the mouth and the esophagus, the BAC can be determined in this manner. Additionally, the blood, once it contains the alcohol, will eventually travel through the lungs so that the alveoli of the lungs give off the alcohol as well. The amount of chemical contained within the alveoli sacs of the lungs is directly related to the amount of it in the bloodstream, making breathalyzers an effective measure of BAC.
Each state has its own legal drunk driving BAC levels, meaning if a person tests their BAC using a breathalyzer and it shows their BAC is above the level, they are arrested on the spot. While in the past, this limit was most notably at 0.10 percent; however, most states have lowered that level so that it is now set at 0.08 percent and anything above that amount is considered to be legally drunk.
The way the breathalyzer translates the amount of BAC in relation to the amount of that is contained within the breath is by a comparison number. The ratio of alcohol in the breath to the what is contained within the blood is 2,100:1. This translates to 2,100 ml of air from the lungs is equal to 1 ml of blood, and the amount contained in both is the same. For example, if someone tests using an alcohol breathalyzer and they show a BAC of 0.05, they have.05 grams of alcohol within their bloodstream. Anything over.08 is considered legally intoxicated or drunk and a person cannot legally drive.
The analyzer used by police patrols can measure the BAC in the same way. These machines have been used for decades. If a person is pulled over for any reason and submits to a breathalyzer test and fails, they are arrested on the spot and their vehicle is typically impounded. However, one thing to keep in mind is that many states also have a law that states that if a driver is asked to submit to a breathalyzer test and the driver does not, he can also be arrested because non-submission is considered an admission of guilt.