But is it accurate enough to say "you're drunk driving"? IIRC at least on this side of the pond, if you're caught you either get fined, or you're taken to the station for a more accurate breath test or a blood test.
In the US, you have the right to request a blood test, but the blood test is not required and the breathalyzer is considered sufficient evidence (again, since the offense is defined in terms of the breathalyzer).
