A breath alcohol test roughly determines how much alcohol is in your blood by measuring the amount of alcohol in the air you breathe out (exhale).

There are various brands of breath alcohol tests. Each one uses a different method to test the level of alcohol in the breath. The machine may be electronic or manual.

One common manual tester requires you to blow up a balloon in one continuous breath until it is full, then release the air into a glass tube. The tube is filled with bands of yellow crystals. The color changes depending on the alcohol content. Count the bands in the tube that have changed from yellow to green. Carefully read the instructions before using the test to make sure you get an accurate result. 

If an electronic alcohol meter is used, follow the instructions that come with the meter.

Wait 15 minutes after drinking an alcoholic beverage and 1 minute after smoking before starting the test.

There is no discomfort.

When you drink alcohol, the amount of alcohol in your blood goes up. This is called your blood-alcohol level. 

When the amount of alcohol in the blood reaches 0.02 - 0.03%, you may feel a relaxing "high."

When that percentage reaches 0.05 - 0.10%, you have reduced muscular coordination, a longer reaction time, and impaired judgment.

Driving drunk is dangerous. A person with alcohol levels of 0.08% and above is considered legally drunk in most states. (Some states have lower levels than others.)

The alcohol content of exhaled air accurately reflects the alcohol content of the blood.

Normal is when the blood alcohol levels are not elevated.

When one band is green, it means that the blood-alcohol levels are between 0.05% or lower. Two green bands mean levels of 0.05% to 0.10%. Three green bands indicate levels between 0.10% and 0.15%.

There are no risks.

The test does not take into account the driving abilities of the test subject. Driving abilities vary among people with the same blood-alcohol levels. Some people with blood-alcohol levels below 0.05% may not be able to safely drive. For occasional drinkers, judgement problems occur at blood-alcohol levels of just 0.02%.

The breath alcohol test helps you to know how much alcohol it takes to raise the blood-alcohol level to a dangerous level. Each person's response to alcohol varies. The test may help you make better decisions about driving after drinking.

Marx J. Rosen's Emergency Medicine: Concepts and Clinical Practice. 5^th ed. St. Louis, Mo: Mosby, Inc.; 2002.