Wisconsin state law requires a judge who convicts a driver of OWI to obtain and install an ignition interlock device on his or her vehicle under certain circumstances. The purpose is to prevent future drunk driving incidents from occurring.

According to FindLaw, it is impossible to start a car equipped with an ignition interlock device without first providing a sample of breath for analysis of blood alcohol concentration. An IID functions similarly to a breathalyzer in that respect.

However, while a breathalyzer just measures BAC, an ignition interlock device can perform the extra step of locking out a driver from starting the car if the blood alcohol level measures above a certain threshold. The minimum BAC that an ignition interlock device will allow is much lower than the legal limit for driving. The former is usually 0.02%, while the latter is 0.08% in Wisconsin.

According to the Wisconsin Department of Transportation, the law requires judges to order an IID under certain circumstances. If a first-time OWI offender had a blood alcohol level of 0.15% or greater at the time of arrest, the judge must order an ignition interlock device upon conviction. Any repeat OWI convictions require an IID.

Refusing to submit to chemical testing is not an effective way to avoid an IID in Wisconsin. In fact, the law requires an ignition interlock device for drivers that fail to comply with a request for a blood or breath sample from law enforcement.

These requirements took effect nearly nine years ago, in July 2010, due to the passage of Wisconsin Act 100.