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 Illinois, the use of an alcohol ignition interlock device (IID) is regulated under the state's DUI laws. Illinois law mandates the installation of an IID for all first-time DUI offenders who wish to obtain driving relief during their suspension period. This is known as the Breath Alcohol Ignition Interlock Device (BAIID) program. The device prevents the vehicle from starting if the driver's BAC is above a preset limit, typically .02 BAC. Installation must be done by a state-approved technician, and the device records data for monitoring purposes. For repeat DUI offenders, the court is more stringent and will generally order the installation of an IID as part of the sentencing. The duration for which an IID must be installed can vary, but it often ranges from 1 to 3 years, depending on the severity of the offense and the offender's history. Despite the effectiveness of IIDs in reducing repeat DUI offenses, compliance rates are not as high as the law intends.