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 New York State, the use of an alcohol ignition interlock device (IID) is mandated for all drivers convicted of a misdemeanor or felony drunk driving offense under Leandra's Law. The law requires the installation of an IID on any vehicle owned or operated by the convicted individual for a period determined by the court, typically for at least 12 months. The device prevents the vehicle from starting if the driver's blood alcohol concentration (BAC) is above a preset limit, usually .02 BAC. Installation must be carried out by a state-approved technician, and the device records data such as breath test results and attempts to tamper with the system. This information is reported to the monitoring company and then to the court. The goal of the IID program is to reduce repeat DUI/DWI offenses, and while it has been shown to be effective, compliance rates are not as high as desired, with only a fraction of those arrested for DUI/DWI actually having an IID installed.