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 Massachusetts, the use of an alcohol ignition interlock device (IID) is primarily governed by state law, specifically under Massachusetts General Laws Chapter 90, Section 24 1/2. The law mandates that IIDs must be installed in the vehicles of all repeat OUI (Operating Under the Influence) offenders as a condition of license reinstatement or issuance of a hardship license. This applies to individuals with two or more OUI offenses. The device prevents the vehicle from starting if the driver's breath alcohol concentration (BAC) is above a preset limit, typically .02 BAC. Installation, monitoring, and maintenance of the IID must be performed by a state-approved provider. The duration for which an IID must be installed varies, but it is generally for a period of two years for second offenders and longer for subsequent offenses. First-time offenders may also be required to install an IID at the discretion of the court, particularly if the case involves aggravating factors such as a high BAC level. The collected data from the IID is reported to the Registry of Motor Vehicles and can be used to monitor compliance with the program. Despite the effectiveness of IIDs in reducing repeat DUI offenses, there is still a gap in the number of devices installed versus the number of individuals arrested for OUI offenses.