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 Michigan, an alcohol ignition interlock device (IID) is a mechanism that can be court-ordered for individuals convicted of driving under the influence (DUI) or driving while intoxicated (DWI). The device prevents a vehicle from starting if the driver's breath alcohol concentration (BAC) is above a preset limit, typically .02 BAC. Installation must be done by a state-approved, certified technician. The IID records data such as breath test results and attempts to tamper with the device, which is reported to the monitoring company and then to the court. Michigan law mandates the use of IIDs for repeat offenders and gives judges the discretion to require them for first-time offenders. The duration for which an IID must be installed can range from one to three years or longer, depending on the court's decision. This requirement can be imposed as a condition of bond or probation. Despite the effectiveness of IIDs in reducing repeat DUI/DWI offenses by about 70%, a relatively small percentage of those arrested for such offenses end up with an IID installed.