In some states, for instance, Vermont, a refusal to submit to a breath test can in and of itself be a crime in addition to the separate crime of Driving Under the Influence (DUI). At the present time, in Illinois, the rules on refusal are different from those in Vermont and some other states.
A DUI arrest begins when a driver has an encounter with law enforcement. The officer might see what he believes to be criminal behavior, including something as basic as a traffic code violation. Or perhaps a driver is slumped behind the wheel of the car being operated, or the officer is otherwise performing a “community caretaking” function.
Sometimes the stop involves an anonymous tip of impaired driving made by a citizen. It could be another driver, a pedestrian or the guy serving food at the drive up window. As long as the tipster is shown to be a “reliable source”, a stop in this circumstance does not violate the United States Constitution’s Fourth Amendment prohibition against unreasonable searches and seizures.