In the 1930s the American chemist Rolla Neil Harger proved that the amount of alcohol in a person's breath is proportional to the amount of alcohol in his or her blood. He used this observation to develop the "drunkometer", an instrument which was used since 1938 by police to measure the level of drivers' intoxication. It used a solution of potassium permanganate in sulfuric acid. This solution oxidizes alcohol; when this reaction happens the purple liquid turns clear – this colour change indicates the presence of alcohol.
A similar oxidation reaction was used by the first breath analysis instrument called "breathalyzer", which was developed by the American chemist Robert F. Borkenstein in 1954. Today, the term has come to be applied more generally to any kind of instrument that analyses a person's breath. Such analyses are used to diagnose diseases as well, for instance to detect the presence of bacteria such as Heliobacter pylori which is thought to be the cause of stomach ulcers.
Ann Newmark,'Breathalyzer', in R Bud, D J Warner (eds), Instruments of Science (New York, London: Science Museum, London, and National Museum of American History, Smithsonian Institution, in association with Garland Pub., 1998), pp 71-3
S J Reiser, ’The science of diagnosis: diagnostic technology‘, in W F Bynum and R Porter (eds), Companion Encyclopaedia of the History of Medicine, Vol. 2 (London: Routledge), pp 826-51