If a motorist is suspected of Driving Under the Influence (DUI), law enforcement will request breath and or blood tests. There are two types of breath tests that must be distinguished.
Before police can make an arrest for DUI, they must have probable cause to believe the driver has committed the offense. In other words, they must gather a sufficient amount of evidence to create a “substantial chance” or “fair probability” of criminal activity. (Illinois v. Gates, 462 U.S. 213 (1983))
This evidence gathering depends in part upon the officer’s observations of the driver’s actions and conduct. This would include the driver’s compliance with safe driving habits and obedience to traffic laws, his or her reaction to the officer’s commands to stop and their maneuvers while pulling over.
After approaching the driver, the officer would note the driver’s physical appearance and actions (bloodshot eyes, odor of alcohol, slurred speech), ability to follow instructions and understanding of time and place. The officer would also be cognizant of the driver’s movements upon leaving the vehicle (staggering, unsteady balance, difficulty getting out of the vehicle).
Once the driver has come back to the squad car-typically within range of a dash cam-the investigating officer will have the driver perform standardized field sobriety tests. First up would be the horizontal gaze nystagumus. In this test, the officer moves a pencil in front of the driver’s eyes looking for certain reactions from his pupils that allegedly are “clues” to intoxication. Continue reading →