Laura Barfield spends a lot of time these days swinging around Florida in her state-issued Chevy to defend the technology that the state uses to catch drunken drivers. As the state's chief defender of the breath-testing Intoxilyzer, her job is to assure everyone that the most challenged of all forensic tests is accurate and reliable. In recent weeks, she has been called to testify in Sarasota, Hillsborough and Port St. Lucie counties. In the weeks ahead, she has dates with courtrooms in Taylor, Lake, Leon, Pinellas and Escambia. It has gotten to the point where the state's breath-testing machine is...