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 Hampshire (NH), an alcohol ignition interlock device (IID) is a mechanism that can be required for drivers convicted of Driving Under the Influence (DUI) or Driving While Intoxicated (DWI). Under NH state statutes, individuals convicted of such offenses may be mandated by the court to install an IID on their vehicles. The device prevents the vehicle from starting if the driver's breath alcohol concentration (BAC) is above a preset limit, typically .02 BAC. Installation must be carried out by a state-approved, certified technician. The IID records data such as engine starts and stops, breath test results, and any attempts at tampering, which is then reported to the monitoring company and potentially to the court. For first-time offenders, the installation of an IID is at the discretion of the judge, while repeat offenders are more likely to be required to install the device. The duration for which an IID must be installed can range from one to three years or more, depending on the court's orders. This requirement can be a condition for bond or probation. Despite the effectiveness of IIDs in reducing repeat DUI/DWI offenses, compliance rates for installation are lower than expected.