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 Connecticut, an alcohol ignition interlock device (IID) is mandated for all offenders convicted of driving under the influence (DUI), even for first-time offenders. The state requires the installation of an IID after a DUI conviction as part of its efforts to prevent repeat offenses. The device prevents the vehicle from starting if the driver's blood alcohol concentration (BAC) is above a preset limit, typically .02 BAC. Installation must be done by a state-approved certified technician, and the device records data such as breath test results and attempts to tamper with the system, which is reported to the monitoring company and then to the court. The duration for which an IID must be installed varies, but it can range from one year for a first offense to three years or more for subsequent offenses. The requirement for an IID may also be a condition for the offender's release on bond or probation. Despite the effectiveness of IIDs in reducing repeat DUI offenses by about 70%, compliance rates are not as high as the law intends, with only a fraction of those arrested for DUI/DWI having an IID installed.