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 Texas, 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. Texas law mandates the use of IIDs for certain driving while intoxicated (DWI) offenders. The Texas Department of Public Safety (DPS) oversees the certification of IID technicians and the installation process. For first-time DWI offenders, the court may require an IID as a condition of bond or probation. However, for repeat offenders or those with a high BAC at the time of arrest, the installation of an IID is mandatory. The duration for which an IID must be installed varies, but it can range from one to three years or more, depending on the severity of the offense and the discretion of the court. Despite the effectiveness of IIDs in reducing repeat DWI offenses, compliance rates are not as high as the law intends, with a significant number of those arrested for DWI not having an IID installed.