Pursuant to Idaho law, officers must have multiple indicators of intoxication in order to initiate a DUI investigation. The first is almost always "driving pattern" (the reason you are pulled over). Beyond this, the three most common indicators listed by Law Enforcement as reasonable suspicion to believe a driver may be intoxicated are: Odor Of Alcohol, Slurred Speech, and Bloodshot/Red/ Watery Eyes. However, these are flawed indicators and may not actual indicate intoxication.
Causes of Bloodshot, Watery, or Red Eyes
Although alcohol consumption may cause an individual's eyes to redden or tear up, unrelated factors may have the same effect. Allergies, exposure to the sun, pollution or smoke and even fatigue can contribute to a person having bloodshot, watery or teary eyes. Some people have eyes that are naturally red or bloodshot. Unless the officer has met the driver before and knows what he or she looks like both sober and intoxicated, any statement about the driver's appearance being indicative of intoxication is just conjecture.
In cross-examining the officer, a skilled DUI attorney will establish that the officer had never seen the Defendant before the time of the arrest. Doing so establishes that the officer had nothing to compare the "signs of intoxication" to—whether their behavior was different at the time of the arrest from any other occasion. This may call the observations of intoxication into question.