Within minutes of drinking alcohol, a person's blood alcohol level starts to rise, and it rises quickly because alcohol is not digested in the stomach like food is. Instead, it is absorbed through the walls of the stomach, goes directly into the bloodstream, and travels throughout the body and to the brain. The amount of alcohol in the blood reaches its highest level about 60 minutes after drinking. However, food in the stomach may increase the amount of time it takes for the blood alcohol to reach its highest level. Most of the alcohol is broken down in the liver. The rest of it is passed out of the body in urine and by breathing.

The amount of alcohol in blood is called the blood alcohol concentration (BAC). It is measured as a percentage that equals the number of milligrams (mg) of alcohol in every 100 milliliters (mL) of blood. The blood alcohol concentration (BAC) can be measured by using a breath test for alcohol.

You can measure your own breath alcohol level with a simple handheld device. The home device is similar to, though not as precise as, the type of test used by police for suspected drunk drivers. If the breath alcohol machine is calibrated and used according to the manufacturer's directions, it can provide an accurate estimate of your blood alcohol level.

There are two different types of devices that can measure the breath alcohol concentration.

• The manual device (such as the Last Call Alcohol Level Indicator or PreVent Alcohol Tester) is a glass tube (or a balloon and a glass tube) containing crystals that change color when exposed to alcohol from your breath. This device is simpler and less expensive than electronic meters.
• The electronic meter (such as the Ensure Personal Alcohol Tester or Pro-Tech 1000 Alcohol Breath Analyzer) shows your blood alcohol concentration (BAC) percentage in a digital display window after you blow into a glass mouthpiece attached to the meter. This type of meter is more expensive than the manual type.

Many bars and restaurants provide their customers with free alcohol breath tests using a device that uses one of these two methods. The devices are also used to monitor people in an alcohol rehabilitation center or hospital.

Self-Test for Breath Alcohol
Results

These tests provide only a rough estimate of your blood alcohol concentration (BAC) at the time of the test.

Manual (glass tube/balloon) test

To read the glass tube breath alcohol test, count the number of yellow bands of crystals that turn green.

• 1 green band roughly corresponds to a BAC of 0.00% to 0.05%.
• 2 green bands roughly corresponds to a BAC of 0.05% to 0.10%.
• 3 green bands roughly corresponds to a BAC of 0.10% to 0.15%.

Electronic breath alcohol meter

Some electronic devices have a "traffic light" display.

• A green light indicates a BAC below 0.04%.
• A yellow light indicates a BAC between 0.04% and 0.08%.
• A red light indicates a BAC above 0.08%.

Some devices, like the Personal Alcohol Level (PAL) meter, display the results as an estimated BAC numerical value.