ABA Family Legal Guide

Automobiles

Your Automobile and the Police

Drunk Driving

How does a breath-testing device work?

The person blows into a small machine, which measures the percentage of alcohol in the person's blood. The law fixes a standard measure, over which a person is deemed to be intoxicated. This measure might be 0.10 (one-tenth of 1 percent blood-alcohol concentration) or 0.08, depending on the state. The law often entitles the defendant to two breath tests that must measure within 0.02 (or some other percentage) of each other.