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Ignition Interlock Device

A breath-testing device wired into a vehicle that stops it starting if the driver has been drinking - required by many states after an impaired-driving conviction as a condition of driving at all.

Informational only - this is not legal advice. These definitions explain general legal vocabulary in plain English. They are not advice about your situation, reading them creates no attorney-client relationship, and the law differs from state to state and changes over time. For advice you can rely on, speak to a lawyer licensed in your state.

What it means

An ignition interlock is a small breath-alcohol analyser installed in a vehicle. The driver blows into it before the engine will start; if the sample is over the device's set threshold the vehicle will not start, and the attempt is logged. Most devices also require "rolling retests" at intervals while driving. The device records every test, every failure and every attempt to tamper with or bypass it, and those logs are reported to the state and can be used to extend the requirement or revoke the driving privilege.

States use interlocks in two ways: as a condition of a restricted licence that lets a person drive during a suspension they would otherwise serve in full, and as a mandatory condition of getting a full licence back after a conviction. Which applies, for how long, and whether a first offence triggers it, is state law. The driver pays for installation, monthly monitoring and removal; many states have a reduced-fee programme for people who cannot afford it.

Driving a vehicle without an interlock while one is required, having someone else blow into the device, or tampering with it are separate offences in most states, and a violation typically resets or extends the required period. The requirement generally attaches to the person, not to one car: any vehicle the person drives must have one.

Where this comes from

Interlock requirements are state law - when one is required, for how long, and what a violation costs. Federal law encourages them indirectly: 23 U.S.C. § 164 conditions a portion of a state's federal highway funds on the state imposing specified minimum penalties on repeat impaired-driving offenders, one of which may be an ignition-interlock requirement, and 23 U.S.C. § 405(d) funds state interlock programmes. Neither creates a requirement on any individual driver.

When people hire a lawyer for this

The questions worth a lawyer's time are whether an interlock can substitute for part of a hard suspension in your state, what the programme actually costs over its full term, and what a logged violation will do - because the device generates the evidence for the next proceeding, and a driver who does not understand the rolling-retest rules can lose a restricted licence without ever having had a drink.

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Part of the LawyerLand plain-English legal glossary. Definitions are written from primary sources - statutes and court rules - and each entry states the authority it rests on, or says plainly when the doctrine is state law with no national rule.

If you cannot afford a lawyer, civil legal aid programmes provide free help with many of these problems: civil legal aid programmes by state.

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