<i>Why? Because in the case of a false positive all you have to do is try again. On the first test you could probably even let this occur immediately.</i>
You're assuming the sensor gave a false positive because of random noise. Not true, it could be systemic, for instance:http://answers.google.com/answers/threadview?id=484275
Cigarette smoke can cause a falsely elevated breathalyzer test. "In all cases, exposing the sensor to any type of smoke or oxygen ion generator will produce false positive test results and inaccurate readings. This includes residual smoke in the lungs of a smoker and ambient smoke that may be present in the immediate area. Do not use an alcohol breath analyzer near any type of ion generator including popular air cleaners and central hvac electronic filtration systems. Smokers must wait a minimum 8-10 minutes after smoking to use a breathalyzer to insure that all residual smoke is absent from the lungs."