You may note, that breathanalisers are not very accurate.
A friend of mine is a Dr turned Dr/statistician who does a lot of work for industry with new drugs and products. He has worked on the law enforcement intoximeters and says that they are highly accurate. They are quite different to the old chemical bag systems and the DIY pellistor which consist of a catalyst and thermistor that burns the ethanol, causing a rise in temperature, like a domestic gas detector. The modern ones use Infra Red light in a reference cell and a sensing cell. I've forgotten exactly the mode of operation -- you could google. They are highly accurate measuring the BA.
What they DON'T do is to show fitness to fly or drive! Nor do they necessarily give an accurate indication of blood alcohol which is why they've changed the law from a max. blood alcohol to a max. breath alcohol or blood alcohol.