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 Virginia, an alcohol ignition interlock device (IID) is a mechanism that prevents a vehicle from starting if the driver's breath alcohol concentration (BAC) is above a preset limit, typically .02 BAC. The Virginia Department of Motor Vehicles (DMV) requires that IIDs be installed by certified technicians. Virginia law mandates the use of IIDs for certain DUI/DWI offenders. For a first DUI offense, the court may require an IID as a condition of restricted driving privileges. For second and subsequent offenses, the installation of an IID is mandatory upon the restoration of driving privileges. The duration for which an IID must be installed varies, but it can be required for a period of 6 months to several years, depending on the severity of the offense and the discretion of the court. The IID program is designed to reduce repeat DUI/DWI offenses and is often a condition for bond or probation. Despite the effectiveness of IIDs, compliance rates are not as high as the law intends, with a significant number of those arrested for DUI/DWI not having an IID installed.