Press the start button—the unit will begin a countdown while the sensor is warmed up. When it reaches zero, take a deep breath a blow into the mouthpiece for 5 seconds. The blowing is similar to blowing out a candle and the user should blow evenly for the entire 5 seconds. Keep blowing at a steady pace for as long as you hear the beeping sound.
The breathalyzer will indicate when to stop blowing (once you hear a click at the end of the beeping sound), and if the sample was not adequate for an accurate reading.
The sensors measure the alcohol level of air in the deep lungs. This value is converted into the corresponding Blood Alcohol Content (%BAC) estimate, which will display on the LCD screen after the breath is analyzed. Testing is most accurate if subjects have not consumed food or alcohol for 15 minutes prior to testing.