Alcohol tester working principle: when the gas sensor does not detect alcohol, added to the A pin 5 level is low, when the gas sensor detects alcohol, its internal resistance becomes low, so that the A pin 5 level becomes high. A for the display pushes the pusher, which has 10 outputs, each output can be driven by a light-emitting diode, the display pushes the A according to the level of the 5th foot high to determine the level of the light-emitting diode in order to light up the level of the light-emitting diode. Sequentially light up the number of light-emitting diode levels, the higher the alcohol content is the greater the number of levels of light up the secondary tube. The upper 5 LEDs are red, indicating that the safe level is exceeded. The following five light-emitting diodes for the green, indicating that the safe level, the alcohol content does not exceed 0.05%. At present, the alcohol tester is mainly used in the transportation industry, underground mining, etc., we most often see is the alcohol tester held in the hands of traffic police.