The state of Iowa sets a standard for alcohol impairment at .08 blood alcohol content level for those who are stopped while operating a motor vehicle. In fact, motorists can even be cited for “wet” reckless driving when the content level is above .05 BAC. However, readings from a field sobriety test are admissible in court, which requires officers to take the suspect to the police station for a BAC level test determined by an official and legally acceptable breath devices. The problem is that these machines often are not operating properly, and even a small detail of reasonable doubt regarding accuracy can result in a case being dismissed.
Breath machines are not perfect by any means, and they must be calibrated regularly for the results to be admissible in a criminal prosecution for impaired driving. The devices are made by multiple companies with minimal standards, and the results are not consistent across all models. Police departments must also maintain these machines with regular documented testing and calibration. Failure to do either can result in inadmissible BAC evidence.
Another issue with breath machines is electrical interference from other electronic equipment in police stations and surrounding buildings. Police radio waves are a particular problem, along with cell phones in the proximity when the machines are in use. Experienced and aggressive drunk driving attorneys can use this issue of upward interference spikes in crafting a comprehensive reasonable doubt defense against the charge.
Another problem is health of the tested suspect. Many people suffer from acid reflux, and alcohol from acids can be detected even when the medical problem is not present at the time of testing. The problem is that the machines are designed to read alcohol levels from the lungs, but those with intestinal problems will have alcohol in their system at all times.