The bactrack singleshot 0.08 % bac tester is perfect for measuring increased levels of alcohol intoxication. The singleshot is based on indicator chemistry that changes color in the presence of breath that contains alcohol. It is laboratory calibrated to turn positive at or above a specific level of alcohol in the breath. Simply squeeze the center of the tube to activate the test, and blow through the singleshot. Based on your blood alcohol content the crystals will either stay yellow indicating a negative result or change to blue/green, indicating a positive result.