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 Maryland, the Motor Vehicle Administration (MVA) oversees the Ignition Interlock Program, which mandates the use of an alcohol ignition interlock device (IID) for certain driving under the influence (DUI) offenders. Maryland law requires drivers with a blood alcohol concentration (BAC) of 0.08 or higher, or those who refuse a chemical test, to participate in the program. First-time offenders may be required to use an IID at the discretion of the court, while repeat offenders or those with a high BAC are typically mandated to install an IID. The device must be installed by a state-approved technician, and the data collected by the IID is reported to the MVA. The duration for which an IID must be installed varies, but it can range from six months to several years, depending on the severity of the offense and the individual's driving record. The goal of the IID program is to reduce repeat DUI offenses and enhance public safety.