A Moment of Science

How Do Breathalyzers Work? And What Do They Measure?

Ever wonder how a breathalyzer test actually works? Find out on this Moment of Science.

Three shots of vodka

Photo: rick (Flickr)

Alcohol is a small molecule that can cross the membranes of your body's cells quite easily.

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.

  • http://www.facebook.com/people/Michael-Kapinus/786909522 Michael Kapinus

    And the breathalyzer was invented by Dr. Robert Borkenstein, an Indiana State Policeman, and a professor at IU, in the 1950's!!

  • http://twitter.com/_LifeGuard _LifeGuard Staff

    A small amount of alcohol that you drink is expelled from the body in your exhaled breath. Breathalyzers measure this alcohol vapor and use it to determine the approximate amount of alcohol in your blood (BAC). If you take a swig of beer and blow into a breathalyzer immediately following the swig, the breathalyzer will pick up residual mouth alcohol and you'll get a falsely high reading. Always wait about 10-15 minutes after your last sip to test yourself. In this way you won't get interference from mouth alcohol.

    For great information on breathalyzers, how they work, DUI and everything related see http://www.lifeguardbreathtester.com

  • http://twitter.com/_LifeGuard _LifeGuard Staff

    A small amount of alcohol that you drink is expelled from the body in your exhaled breath. Breathalyzers measure this alcohol vapor and use it to determine the approximate amount of alcohol in your blood (BAC). If you take a swig of beer and blow into a breathalyzer immediately following the swig, the breathalyzer will pick up residual mouth alcohol and you'll get a falsely high reading. Always wait about 10-15 minutes after your last sip to test yourself. In this way you won't get interference from mouth alcohol.

    For great information on breathalyzers, how they work, DUI and everything related see http://www.lifeguardbreathtester.com

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  • http://twitter.com/_LifeGuard _LifeGuard Staff

    This article is incorrect in several ways:

    1) If you take a drink just before taking a breathalyzer test the breathalyzer will pick up what's called “residual mouth alcohol” and it will be measured. Breathalyzer users are always advised to wait 10-15 minutes after a sip of alcohol to test themselves.
    2) Breathalyzers don't pick up alcohol in your lungs, they pick up alcohol exhaled in your breath.
    3) Alcohol does not go everywhere in your body in equal concentrations. About 10% of the alcohol you consume is exhaled in your breath.

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  • Saraphina

    2) But doesnt the air from your breath when you blow into the thing come from your lungs?

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