An alcohol ignition interlock device (IID) is a breath-test device that is connected to a vehicle’s ignition. A vehicle with an IID installed will not start unless the driver blows into the interlock and has a blood alcohol concentration (BAC) below a limit set by the court—usually .02 BAC. IIDs must be installed by a certified technician approved by the state’s department of motor vehicles (DMV). The IID will collect data (engine starts and stops, breath test results, and tampering attempts) and report it to the monitoring company, which will report it to the court.

IIDs reduce repeat offenses for DUI/DWI by approximately 70% when installed. Laws vary from state to state and courts have significant discretion, but a judge may order a person convicted of a first DUI/DWI offense to install an IID and will order a person convicted of a second or third DUI/DWI to install an IID. Courts will often order an IID installed on the defendant’s vehicle as a condition of bond (to be released from jail) and of probation (following jail or prison time, or in lieu of any or more jail or prison time). The court may order the defendant’s IID to remain on the vehicle for 1-3 years or more.

Despite these laws and programs, only about one-fifth of those arrested for DUI/DWI have an IID installed.

In Wisconsin, the use of an alcohol ignition interlock device (IID) is mandated by state law for certain individuals convicted of operating while intoxicated (OWI), which is Wisconsin's equivalent of DUI/DWI. The requirement for an IID is generally imposed on all repeat OWI offenders, first-time offenders with a blood alcohol concentration (BAC) of 0.15 or higher, and individuals who refuse to submit to a BAC test. The court may also require an IID for other first-time offenders at its discretion. The device must be installed on every vehicle owned or operated by the offender, and the duration for which the IID must be maintained ranges from a minimum of one year to the entire period of the offender's driving restrictions. The installation must be carried out by a state-approved technician, and the device records data for monitoring purposes. Failure to comply with IID requirements can result in extended driving restrictions and other penalties. Despite the effectiveness of IIDs in reducing recidivism, compliance rates are not as high as the law intends.