Breathalyzer (Breath Test Alcohol Detector) - with schematic

Today I took a look inside a cheap Chinese breath alcohol test device (breath analyzer). It contains an alcohol sensor and a simple indication circuit with 3 LEDs. The LEDs indicate 3 levels of breath alcohol content: no alcohol, 0.02% BAC and 0.05% BAC). It also has a torch function and runs on 2 AAA batteries. During this teardown I managed to reverse engineer the full schematic and explain how does it work. This device seems to work well, but you still don't have a 100% guarantee of accuracy. Even if it shows no alcohol, it does not guarantee you can drive safely.

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