When it comes to drinking and driving, there are two things that most people know: 1.) this form of reckless behavior is illegal in all states and 2.) in order to avoid a DUI charge, your blood-alcohol level must be less than .08 if you are over the age of 21.

As you may already know, police can determine your blood-alcohol level using one of two methods: a breath test or through chemical testing. While chemical testing is relatively easy to figure out how it works, Breathalyzers are more of a mystery to many people. In this week’s post, we will look at how these devices work to help answer the question: how does a Breathalyzer determine intoxication?

Have you ever smelled someone’s breath after they have been drinking? Did it smell like alcohol? That’s because alcohol is absorbed into the bloodstream then, when the blood passes through the lungs, it evaporates and is exhaled on a person’s breath. This concentration of alcohol vapor is directly related to the alcohol in your blood, meaning if police have a way of measuring it, they can get an idea of how intoxicated you are.

There are three types of breath tests and they are:

Breathalyzer. This test uses a chemical reaction to determine a person’s BAC. A sample of a person’s breath is sent into a vial filled with specific chemicals. Any alcohol in a person’s breath will react with the chemicals causing a color change. The more alcohol is present, the more pronounced the color change will be.

Intoxilyzer. This test uses infrared spectroscopy to determine blood-alcohol content. This is done by focusing infrared light at a breath sample. The device measures how the IR light is being absorbed by the molecules in the air and the amount of absorption. These measurements tell an officer not only if a person has been drinking but how much has been absorbed into the person’s bloodstream as well.

Alcosensor III or IV. This test uses fuel-cell technology in breath tests. When a person exhales into the device, alcohol molecules oxidize, producing protons, electrons and acetic acid. The electrons and protons create an electrical current. The greater the current, the more alcohol is present.

Source: How Stuff Works, “How Breathalyzers Work,” Craig Freudenrich, Ph.D., Accessed Oct. 8, 2014