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 Maine, an alcohol ignition interlock device (IID) is a mechanism that can be court-ordered for individuals convicted of operating under the influence (OUI), which is Maine's equivalent of DUI/DWI. The device prevents a vehicle from starting if the driver's breath alcohol concentration (BAC) is above a preset limit, typically .02 BAC. Maine law mandates that IIDs must be installed by a state-approved technician. The device records data such as breath test results and attempts to tamper with the device, and this information is reported to the monitoring agency and potentially to the court. For a first OUI offense, the installation of an IID is at the discretion of the court, but it becomes more likely for repeat offenses. The duration for which an IID must be installed can vary, but it is often required for a period ranging from one to several years, depending on the severity of the offense and the individual's prior record. Despite the effectiveness of IIDs in reducing repeat OUI offenses, there is a gap between the number of individuals arrested for OUI and those who actually have an IID installed.