DUI or driving under the influence of alcohol or drugs is illegal in every state. It is illegal in every state to operate a motorized vehicle with a BAC or blood alcohol concentration of 0.08% or higher, but drivers may be arrested for DUI even if their BAC is below the legal limit if they fail a field sobriety test or they are unable to safely operate their vehicle. Common signs of DUI can include: difficulty answering questions, slurred speech, droopy eyes, blood-shot or watery eyes, flushed face, stumbling or the smell of alcohol on the driver's breath.