Breath alcohol testing devices, commonly known by the term for one type of device – Breathalyzer, measure how much alcohol is currently in the blood.

Blood alcohol concentration (BAC) is measured by blowing into a breath alcohol device. The results are given as a number which shows the level of alcohol in the blood. The legal limit for being considered impaired while driving is .08.

However, US Department of Transportation regulations consider a .04 a positive alcohol test requiring removal from driving or other safety-sensitive tasks. A .02 under DOT regulations can require removal from tasks for a certain period of time.

Blood alcohol tests show current levels of impairment or intoxication not past use.