Give Now  »

Noon Edition

How Do Breathalyzers Work? And What Do They Measure?

If a police officer sees you driving in a reckless manner, chances are you'll be pulled over and asked to breathe into a special machine that measures your blood alcohol content. But how can your breath reflect how much alcohol is in your blood?

Alcohol's Affect On The Body

The answer has to do with how alcohol is distributed throughout your body. Alcohol is a very small molecule that can cross the membranes of your body's cells quite easily. Cellular membranes do not block the movement of alcohol molecules throughout the body.

Once you take a drink, alcohol is absorbed into your blood stream and then distributed to various tissues. In the process of distribution, alcohol experiences few barriers and goes just about anywhere in equal concentrations. One of the places it ends up is in the air of our lungs.

What Does A Breathalyzer Measure?

A breathalyzer measures the amount of alcohol in your lungs. If you had taken a single swallow of beer right before the breathalyzer test, your breath might smell of alcohol, but the test would indicate that you were not intoxicated.

This is because the breath you would bring up from your lungs would not have any alcohol in it, even though the breath in your mouth might.

Because the alcohol content of air in your lungs accurately reflects the alcohol content in the blood stream, law enforcement officers can use this information to know whether or not to take the keys from a driver who seems to be intoxicated.

Support For Indiana Public Media Comes From

About A Moment of Science