Are Ignition Interlock Devices Effective?
Yes. Authoritative reviews find that ignition interlock devices substantially reduce repeat impaired-driving offenses while they are installed. The strongest evidence does not show that the same benefit reliably continues after removal, so it is important to distinguish the in-use effect from longer-term behavior change.
An ignition interlock device, or IID, measures a driver’s breath alcohol concentration before allowing a vehicle to start. It can also require additional breath tests during a trip. This creates an immediate barrier to driving after drinking while helping the driver document compliance with program requirements.
Evidence at a Glance
- CDC, Increasing Alcohol Ignition Interlock Use, updated April 24, 2024: IIDs reduce repeat DWI offenses by about 70% while installed.
- Community Preventive Services Task Force, Alcohol-Impaired Driving: Ignition Interlocks: two systematic reviews covering 15 studies found a median 67% reduction in re-arrest while devices were installed. Re-arrest rates returned toward comparison-group levels after removal.
- California State Transportation Agency evaluation, December 31, 2024: installing an IID within two years of arrest reduced measured recidivism outcomes, including future DUI arrests, crashes, and injury crashes, in the California evaluation.
How Do Ignition Interlocks Reduce Repeat Impaired Driving?
An IID connects to a vehicle’s ignition system. Before the engine can start, the driver provides a breath sample. If the sample is above the program’s preset threshold, the vehicle will not start. Programs may also require rolling retests after the vehicle is running. The device records events so the appropriate monitoring authority can review compliance.
The main benefit is practical and immediate: the device restricts vehicle use when a breath sample is above the threshold. That is different from guaranteeing sobriety or changing behavior after the device is removed. For a closer look at the technology and routine, learn how an IID works.
What the Evidence Does and Does Not Show
The evidence is strongest for the period when an IID is installed. The Community Preventive Services Task Force found a substantial reduction in re-arrest during installation, but it also found that re-arrest rates tended to return toward comparison levels after removal. An IID is therefore best understood as a tool that directly limits impaired vehicle starts and supports compliance during the required period, not as a guarantee of permanent behavior change.
The CDC also reports that, during 2001 through 2019, all-offender IID laws were associated with 26% fewer alcohol-impaired drivers in fatal crashes. Laws covering repeat and high-BAC offenders were associated with 20% fewer. These are law-level associations across populations. They do not prove that every driver or jurisdiction will experience the same result.
What Makes an Ignition Interlock Program Effective?
Effective use depends on correct installation, regular service, reliable testing, and following every requirement from the court or licensing authority. Drivers should take each requested test as directed, attend scheduled calibration or service visits, and contact their provider if they have questions about a reading or device operation. An IID can sometimes register alcohol from sources other than an alcoholic drink, so drivers should follow program instructions and document concerns rather than assuming false positives are impossible.
Professional installation helps ensure the device is connected and configured for the vehicle. Ongoing appointments keep the device working and provide the records required by the applicable program. To prepare for service, review what to expect during ignition interlock installation.
Frequently Asked Questions
How much do ignition interlocks reduce repeat DWI offenses?
The CDC says IIDs reduce repeat DWI offenses by about 70% while installed. The Community Preventive Services Task Force found a median 67% reduction in re-arrest during installation across the studies it reviewed. These findings describe groups and do not guarantee an outcome for an individual driver.
Do ignition interlocks keep working after they are removed?
The strongest reviews do not show that the reduction reliably continues after removal. The Community Preventive Services Task Force reports that re-arrest rates returned toward levels seen in comparison groups after devices were removed.
Can an ignition interlock produce a false positive?
An IID is designed to measure breath alcohol, but alcohol from certain foods, drinks, or products may affect a reading. Devices do not eliminate every possibility of an unexpected result. Follow your program’s instructions, allow time before retesting when directed, and contact your provider if you have concerns.
Where can I learn about installation and next steps?
Review what to expect during ignition interlock installation, then contact Budget IID to discuss availability and the requirements that apply to you.
Ready to Take the Next Step?
Budget IID provides court-approved ignition interlock devices, professional installation, and support for drivers working to meet their requirements. Service options vary by area. Get started with Budget IID or call (877) 379-1876 to ask about your next step.