Breath-analysis machines detect and measure the alcohol present in air that is breathed out. When an individual drinks alcohol, the alcohol crosses from the intestine into the bloodstream. When the blood circulating around the body gets to the lungs, some of the alcohol in the blood crosses into the air contained in the tiny sacs of the lungs. The air that is breathed out of the lung will contain alcohol that can be measured by breath-analysis machines.

Researchers have determined the ratio of breath alcohol to blood alcohol. The Breathalyzer result allows the tester to estimate the concentration of alcohol in the blood. Blood alcohol concentration (BAC) is approximately 2,300 times greater than breath alcohol concentration, with some variation among individuals. Breath-alcohol analysis is quick and noninvasive. This makes the Breathalyzer breath-test machine a useful tool for law enforcement agencies to monitor drinking and driving.

If a person's BAC...