When performing a direct breath alcohol test, the subject blows directly into the testing instrument using a mouthpiece. When performing a passive test, the device is held in front of the subject as they are talking, or they are asked to blow at the device. No mouthpiece is used with a passive device.
A direct breath alcohol test can measure intoxication level. A passive breath alcohol test can detect the presence of alcohol in a subject, but cannot necessarly measure the intoxication level.