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How Does Breathalyser Alcohol Testing Work?

Many people wonder how alcohol testing with the breath can possibly be correlated with the amount of alcohol in your bloodstream - especially if you've drunk plenty of water and had something to eat in the meantime. However, alcohol testing with breath analysers is highly accurate - here's how it works.

You drink alcohol

The amount of alcohol you drink is constant, however, individual variables will affect the speed at which it is absorbed into the body.

Absorption occurs

Alcohol is quite a small molecule, and remains unchanged (unlike the larger proteins and carbohydrates in the food we eat) as it is absorbed into your bloodstream via the digestive tract and small intestine.

Alcohol circulates

The alcohol moves around your body, affecting the way signals are sent around your brain - causing the effects of alcohol as we know them.

It reaches the lungs

When the alcohol circulating in your blood reaches the lungs, it will readily diffuse out of the blood, just as carbon dioxide does. Therefore, if you have alcohol in your blood you will also exhale alcohol, which can be detected by alcohol testing.

Problems with alcohol testing

Alcohol testing is based on sound and well-proven biological mechanisms. However, problems can occur with alcohol testing because of two assumptions:

  • Alcohol detected on the breath may not have come from the bloodstream, and
  • The conversion of amount of alcohol measured to percentage of blood alcohol can vary among individuals.

Still, alcohol testing with our current tools is able to give us BAC readings that are generally accurate to +/-10%. This is accurate enough for police to require blood alcohol testing, if you 'blow' above a certain amount.