In Arizona, if you are pulled over by a police officer who suspects that you may have been driving under the influence of alcohol that officer has different ways to determine in his or her judgment whether you have in fact been engaged in drunk driving. Most of the time, the focus is on the result of a blood or breath alcohol test and its .08 threshold. But that number is not always the final arbiter when making the final decision.
What happens, for example, if you test at .07? Does that automatically mean that you are not legally under the influence of alcohol for drunk driving purposes? Not necessarily. Police who still suspect you of drunk driving have at least one other way to see if you have been drinking too much: the field sobriety test.
Anyone who has seen a reality program on television that follows the activities of law enforcement officers has likely seen field sobriety tests in action; often, given the poor performance of the people being subject to such tests. But there are scientific bases for these tests.
Take, for example, the "horizontal gaze nystagmus." This is the test in which the officer has you track an object, like a pen, from one side to the other using only your eyes. The basis for this test is that alcohol exaggerates the otherwise normal eye "jitter" that takes place when your eyes reach the maximum side angle.
Or the "walk-and-turn," instead of being a test of coordination, this test actually measures your ability to perform subject to distractions to your focus of attention, something that people under the influence of alcohol can have trouble coping with.
The effectiveness of field sobriety tests depends, like with blood or breath tests, on the training and knowledge of the officer performing the test. If they are not performed properly, the results can be subject to challenge in court.
An attorney familiar with these tests will know how to find out whether they have been properly administered, as well as with other areas in which the police must carefully follow prescribed procedures when making a legal determination of whether to properly arrest you for drunk driving.