How Does a DUI Breath Test Work?
Accordingly to Boyles Law, the amount of alcohol in a liquid (like your blood) is the same as the amount of alcohol in the air hovering just above your blood. There is only one place in the universe where air hovers just above your blood, and that is deep in your lungs where there are structures called alveoli. When you blow into the straw connected to the breath testing machine, you are blowing air from your lungs into a chamber within that machine. Once enough air gets in there, the machine shines a light through the air from your lungs. There is a photo cell on the far wall of the chamber that measures how much light comes through the air and how much is blocked by the alcohol in your breath. The more light that gets blocked, the higher the concentration of alcohol the device will read.
