In many states this isn’t a “trick”: a 20 minute observation period is codified in law before the evidentiary breath test is used to ensure that the test is acc

In many states this isn’t a “trick”: a 20 minute observation period is codified in law before the evidentiary breath test is used to ensure that the test is accurate. See for example this publication from the Wisconsin bar association - https://www.wisbar.org/newspublications/wisconsinlawyer/pages/article.aspx?Volume=88&Issue=1&ArticleID=23792 https://www.wisbar.org/newspublications/wisconsinlawyer/page... > The protocol for an Intoximeter test, by contrast, is much more involved. A valid test on the Intoximeter must be preceded by a 20-minute observation period (to ensure the subject does not burp, belch, regurgitate, and so on). Additionally I would be surprised if you can produce case law around estimation and extrapolation of BAC being legally acceptable in courts: in most cases the opposite is true. For example, Romano v. Kimmelman: > In drunk driving prosecutions a substantial burden of proof to establish the competence or admissibility of the results of the breathalyzer test is appropriate because of the serious consequences of the breathalyzer reading in such prosecutions. In general the best advice for people pulled over by the police is to refuse any preliminary breath test and refuse any field sobriety tests. Those tests exist to establish probable cause to take you to the police station for an evidentiary test. Your state law may of course vary but in mine refusal of either roadside test is not illegal and the refusal is not admissible in court. If you are taken to the police station for a test because the police have probable cause you almost certainly cannot refuse that test without violating state law; this is where a good lawyer challenging probable cause for the stop/search and the testing procedures comes into play.