What is the chemical reaction that occurs in a breathalyzer?
Well, in the old days, they used orange crystals of potassium dichromate.
That is breath alcohol would be oxidized by the orange dichromate to give green
These days, they use solid state devices to test blood alcohol. I am told that when someone is nabbed for drink driving (using these tests) that they take a blood sample later so that they are certain of the alcohol level.