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.

Looking for a lawyer rather than a definition? Skip to the state-by-state list of DUI-DWI law firms.

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 license that lets a person drive during a suspension they would otherwise serve in full, and as a mandatory condition of getting a full license back after a conviction. Which applies, for how long, and whether a first offense triggers it, is state law. The driver pays for installation, monthly monitoring and removal; many states have a reduced-fee program 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 offenses 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

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 program 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 license without ever having had a drink.

Worried about the cost? A lawyer can be hired for one part of a case only (limited-scope representation), may be paid from what a claim recovers (contingency fee), or may be free through a pro bono program or legal aid; a court can also waive its own filing fees.

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Choose your state to see DUI-DWI law firms in the city where we list the most; your city may be under “other cities”, A to Z.

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Related terms

Entries on the same subject:

• DUI / DWI (Impaired Driving)Driving while impaired by alcohol or drugs - a charge that almost always runs as two separate cases at once, one criminal and one over the license.
• Field Sobriety TestsThe roadside balance, coordination and eye-movement exercises an officer uses to build probable cause for an impaired-driving arrest - usually voluntary, and never the same thing as the chemical test that follows.
• Implied Consent and Administrative License SuspensionThe rule in every state that by driving you have agreed to a chemical test for alcohol or drugs after a lawful arrest - and the license suspension that follows a refusal or a failed test, separately from any criminal case.

Other entries in the same area of law, each written from the same primary sources.

• CDL DisqualificationThe federally defined list of offenses that take away a commercial driver's license - including offenses committed in a personal car, and a lower alcohol limit than applies to other drivers.
• Contesting a Traffic TicketWhat a moving violation citation actually is, the difference between an infraction and a traffic misdemeanor, and the procedures - hearing, written defense, traffic school - for answering one.
• Driving Record PointsThe system most states use to score moving violations against a driver's record, with a license suspension when the total crosses a threshold - and an interstate compact that makes an out-of-state ticket count at home.
• Event Data Recorder (Vehicle Black Box) EvidenceThe crash data a modern vehicle records about itself in the moments before an impact - what the federal standard requires it to capture, who owns it, and who may retrieve it.
• Hours-of-Service Rules (Commercial Trucking)Federal limits on how long a commercial driver may drive and work, and the electronic records that show whether those limits were kept.
• Leaving the Scene of an Accident (Hit and Run)The legal duties every state imposes on a driver involved in a crash - to stop, to exchange information and to help anyone hurt - and the separate criminal offense of driving away instead.
• Lemon Law and Warranty RightsRules that entitle a buyer to a refund or replacement when a new vehicle has a defect the manufacturer cannot fix in a reasonable number of attempts.
• Negligent Entrustment (Lending a Vehicle)The claim against a person who lent a car to someone they knew, or should have known, was unfit to drive it - the owner's own negligence, separate from the driver's.
• No-Fault Car InsuranceA system in which your own insurer pays your medical bills after a crash regardless of who caused it - used in a minority of states, and it limits when you can sue.
• Odometer Fraud and the Odometer DisclosureRolling back or replacing an odometer to hide a vehicle's true mileage is a federal offense, and every transfer of a vehicle must come with a written mileage statement the buyer can sue over if it is false.
• Permissive Use (Insurance Follows the Car)Which policy pays when someone drives a borrowed car with the owner's permission - the omnibus clause, the exclusions that defeat it, and the owner-liability statutes some states add.
• Policy LimitsThe maximum an insurance policy will pay - and usually the real ceiling on what a claim is worth, whatever the injury.
• Rideshare Accident Insurance (App Periods)Which insurance applies when a rideshare vehicle is in a crash depends on what the driver's app was doing at that moment - the three periods state transportation network company laws define, and the gap that personal policies leave.
• Salvage and Rebuilt TitlesThe title brands a state applies to a vehicle an insurer has declared a total loss, what a rebuilt brand means, and the federal database built to stop a branded title being washed clean in another state.
• SR-22 and Financial Responsibility FilingsThe certificate an insurer files with the state to prove a high-risk driver is carrying the required liability coverage - what triggers it, why it is not itself insurance, and what happens if the policy behind it lapses.
• Tire Defect Claims (Tread Separation and Blowouts)Injury claims after a tire fails, where the question is whether the tire was defectively made or designed, was too old or was recalled, rather than only how the driver reacted.
• Total Loss and Diminished ValueWhat happens when an insurer decides a damaged vehicle is not worth repairing - and the separate claim for a repaired car that is now worth less.
• Uninsured and Underinsured Motorist CoverageCoverage on your own policy that pays when the driver who hurt you had no insurance, or nowhere near enough - and it is the coverage people most often discover they declined.
• Used Car Buyers Guide (FTC Used Car Rule)The window sticker a dealer must display on every used vehicle offered for sale, stating whether it comes with a dealer warranty or as is - and why the sticker overrides the contract.
• Vehicle Safety RecallA manufacturer's federally supervised obligation to notify owners of a safety defect and fix it free of charge - and the rules on what a dealer may sell with a recall still open.

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