Breath analyzers aren’t exactly accurate. There’s a bunch of things that can give them false positives, they often aren’t properly calibrated, and the science behind them is kinda shaky. They got challenged often enough in certain states that in at least one state if an officer has you breathe in a machine and that machine produces a number higher than the legal BAC limit, that’s proof of DUI regardless of what the machine may or may not do to result in that number.
Meh, they do work. They just measure stress response, not truthfulness. The idea being that you’ll have a heightened stress response to a question you are lying about the answer to, which may or may not be accurate depending on individual and situation.