Glossary

Ignition interlock device

An in-car breath tester that keeps the engine from starting if it detects alcohol, often required after a DUI conviction.

Also called: IID, ignition interlock, breathalyzer interlock, car breathalyzer

An ignition interlock device (IID) is a breath-alcohol tester wired into a vehicle's ignition. The driver must blow into it before starting the car, and the engine will not start if the reading is over a preset limit. Most devices also require random retests while driving and log the results, and many take photos to confirm who is providing the sample. A state-approved vendor installs the device, services it on a schedule and reports results to the state or court.

States use interlocks after DUI offenses, either as a condition for restricted driving privileges during a suspension or as a mandatory penalty. Many states require one for all DUI offenders, including first offenders, while others require it only for repeat offenses or high blood alcohol levels. The required period ranges from months to years, and the driver usually pays for installation, monthly monitoring and removal.

The device itself does not change your insurance coverage, but the conviction behind it does. Drivers who need an interlock are typically also under an SR-22 or FR-44 requirement and are rated as high risk. Answer your insurer's questions about the conviction and your license status truthfully. Violations the device records, such as failed or skipped retests, can extend the requirement.

Last reviewed October 4, 2026

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Related terms

DUI Driving while impaired by alcohol or drugs, an offense that brings license penalties, possible SR-22 or FR-44 filings and steep insurance increases. SR-22 A form an insurer files with the state to certify that a high-risk driver carries the required liability coverage, often for about three years. High-risk driver A driver insurers expect to cost more in claims because of a DUI, tickets, crashes, a coverage lapse, little experience or similar factors. Major violation A serious driving offense, such as DUI, reckless driving or driving with a suspended license, that brings large surcharges and can lead to nonrenewal. FR-44 A certificate filed by an insurer in Florida or Virginia proving that a driver convicted of certain DUI offenses carries higher-than-minimum liability limits.

Related guides

Car insurance after a DUI What a DUI does to your car insurance: surcharges, possible nonrenewal, SR-22 or FR-44 filings, how long it counts, and how to stay insured.