If a court or your state’s motor vehicle department has ordered a breathalyzer in your car after a DUI, you’re dealing with an ignition interlock device: a leased in-car breath tester wired to your starter that keeps the engine from turning over if it detects alcohol on your breath. More than 30 states now require one even for a first offense, and you’ll typically live with it for six months to several years, pay for it out of pocket, and face strict rules that can extend the requirement if you miss a calibration or fail a test you can’t explain.
How the Device Works Every Time You Drive
Before the car starts, you blow into a handheld mouthpiece for about five seconds. The device reads your breath alcohol and either releases the starter or holds it locked through a cooldown period before you can try again.
The fail threshold is far lower than the 0.08 BAC that defines a standard DUI. Most states set their interlock devices to flag at 0.02 or 0.025 BAC. A few states use 0.03 or 0.05, but 0.02 is the federal testing set point that NHTSA uses to certify devices, which effectively puts a floor under state programs.1Federal Register. Model Specifications for Breath Alcohol Ignition Interlock Devices In practical terms, one drink can be enough to lock your car.
The device keeps testing after you’re rolling. At random intervals it prompts a rolling retest and gives you a few minutes to provide a sample. Failing a rolling retest does not shut the car off mid-road. The horn honks and the lights flash until you pull over and turn off the ignition, and the failed reading is logged and transmitted to your monitoring authority. Ignoring the prompt or failing repeatedly can trigger a temporary lockout, or in some states a permanent lockout that requires a tow to the service center.
Many newer units include a camera that photographs you during each test to confirm you’re the one blowing rather than a passenger or a friend. Camera-equipped devices are increasingly standard as states tighten compliance rules.
How Long You’ll Have It
Currently, 31 states and the District of Columbia require ignition interlocks for all DUI offenders, including first offenders.2National Conference of State Legislatures. State Ignition Interlock Laws The rest generally reserve mandatory interlocks for repeat offenders or high-BAC first offenders, though judges in many of those states can order one in any DUI case.
The federal government pushes states toward all-offender laws through highway safety grants. Under 23 U.S.C. § 405(d), states get additional funding when they require interlocks for at least 180 days after an impaired-driving conviction and use a compliance-based removal program.3Office of the Law Revision Counsel. 23 USC 405 – National Priority Safety Programs Actual periods vary widely:
- First offense, standard BAC: typically six months to one year.
- First offense, high BAC (0.15+): often one year or longer.
- Second offense: usually one to three years.
- Third or subsequent offense: two years to indefinite.
The requirement can come from two directions. A court may order it as part of your sentence or probation. Separately, your state’s motor vehicle department may impose it as a condition of reinstating your license or issuing a restricted one. Often both apply, and you need clearance from both before the device can come off.
What It Costs
You pay for the interlock yourself. The device is leased, not purchased, and the charges stack across several categories.
- Installation: $70 to $150 at a state-approved service center.
- Monthly lease and monitoring: $50 to $120 per month, covering the rental and data transmission to your monitoring authority.
- Calibration: required every 30 to 90 days depending on state rules. Roughly $25 per visit, though some providers bundle it into the monthly fee.
- Removal: typically $50 to $100 when you complete the program.
A six-month interlock usually runs $500 to $900 total for the device. Twelve months pushes that to $800 to $1,600 or more depending on the provider and state. Those numbers don’t include reinstatement fees, court fines, or insurance costs.
Some states run indigent funds that subsidize interlock costs. New Mexico’s Interlock Device Fund covers up to $50 for installation, $30 per month for active use, and $50 for removal.4New Mexico Department of Transportation. Ignition Interlock Program Other states offer sliding-scale fees through approved providers. If cost is a barrier, ask your attorney or the court about assistance before assuming you have no options.
Insurance, SR-22, and Reinstatement Fees
The device is only one layer of financial fallout. After a DUI conviction, auto insurance premiums typically rise sharply. Industry data shows the average driver’s premiums roughly double, with increases of 50 to 300 percent common depending on state and insurer. Installing the interlock does not lower your rate; insurers price on your driving record.
Nearly every state also requires an SR-22 filing (or an FR-44 in some states), a certificate your insurer sends the motor vehicle department confirming you carry the required minimum liability coverage. The filing requirement typically lasts three to five years from conviction, and if the policy lapses during that period, the insurer notifies the state immediately and your license is suspended again. There’s no grace period.
License reinstatement fees add another line item, ranging from about $20 in some states to over $1,000 in others, with most between $100 and $500. Some states stack administrative charges for interlock oversight, drug surcharges, or victim funds on top. For a first offense with a 12-month interlock, total out-of-pocket costs commonly reach $5,000 to $10,000 or more once you add fines and treatment programs.
False Positives and How to Avoid Them
Interlocks are sensitive enough to catch residual alcohol from things you didn’t drink. Mouthwash is the most common source, since many brands contain 14 to 27 percent alcohol. Hand sanitizer vapors, certain cough medicines, energy drinks, and food particles trapped in dental work can register. A false positive still gets logged, reported, and potentially treated as a violation.
The practical defense: rinse your mouth with water before every test, avoid alcohol-based mouthwash entirely, and wait at least 15 minutes after eating or using any oral product before blowing. If you get a reading you believe is a false positive, most devices allow a retest after a short lockout of a few minutes. A clean retest within that window generally prevents the failed reading from being counted as a formal violation, though reporting rules vary by state.
Medical conditions like acid reflux or uncontrolled diabetes can produce mouth alcohol or acetone. The NHTSA model specifications require devices to pass an acetone interference test at low BAC levels, so properly calibrated units should distinguish acetone from alcohol.1Federal Register. Model Specifications for Breath Alcohol Ignition Interlock Devices Older or poorly maintained devices sometimes still flag false results. If you have a documented condition, put a letter from your doctor on file with your monitoring authority before any dispute comes up.
Restricted License Rules and the Employer Vehicle Exemption
In most states, the interlock comes with a restricted license rather than a full one. Some states restrict driving to specific hours or to work, school, and medical appointments. Others issue a full-hours license marked with an interlock restriction code that tells law enforcement the device is required. Either way, driving any vehicle without an interlock, including a friend’s car, violates the restriction and can carry the same penalties as driving on a suspended license.
About 20 states offer an employer vehicle exemption. If your job requires you to drive a company-owned vehicle, the employer can submit documentation authorizing you to operate it without an interlock installed. The exemption applies only to business driving during work hours. You can’t use the company vehicle to commute, the vehicle must be owned or leased by the employer, and the exemption doesn’t apply to self-employed drivers. Your personal vehicle still needs the device.
Tampering and Circumvention Penalties
Getting caught bypassing, disabling, or tampering with an interlock creates problems worse than the original DUI. Every state treats circumvention as a separate offense.
- Fines from a few hundred dollars up to $5,000 or more.
- Jail time, often up to six months to a year in states that classify tampering as a misdemeanor.
- Extended interlock period, commonly six months to a year added to the original requirement.
- License revocation in some states, leaving you with no legal driving privileges at all.
Having someone else blow into the device counts as circumvention and is one of the most heavily penalized violations. Camera-equipped devices have made it harder to attempt, and the consequences reach both you and the person who provided the sample.
Unintentional issues can also trigger a tampering flag. A mechanic disconnecting the battery without following the proper procedure, or an electrical problem that cuts power to the device, can generate a tampering event. Keep documentation from any mechanic who works on the car, and notify your service provider before any maintenance involving the electrical system.
Calibration Appointments and Lockouts
Calibration appointments are mandatory every 30 to 90 days depending on the state. Miss one and many devices enter a lockout that prevents the car from starting. You’ll need it towed to the service center to reset, at your expense. Set multiple reminders. A missed appointment is one of the most common ways people accidentally extend their interlock period, because states often treat it the same as a violation.
A permanent lockout, whether from a missed service visit, repeated failed tests, or an unaddressed recall notice, means the car won’t start until a service provider physically resets the device. Towing, service fees, a report to your monitoring authority, and in some states additional months added to the requirement all follow.
Day to day, the device adds two to three minutes of warmup every time you start the car. Budget five to ten extra minutes before every drive, more in cold weather. Rolling retests happen in traffic and at highway speeds; you have a few minutes to blow, so you’re not testing while merging, but passengers will notice and the retests are audible.
Getting the Device Removed
Early removal depends entirely on your state. Some states allow performance-based early removal after a violation-free stretch, often at least 40 to 50 percent of the original term. Others set a fixed minimum with no early release, regardless of your record. The federal grant standard under 23 U.S.C. § 405(d) requires a minimum consecutive violation-free period of at least 40 percent of the required installation time before removal.3Office of the Law Revision Counsel. 23 USC 405 – National Priority Safety Programs
Where early removal is available, the process typically involves confirming you’ve met the minimum time and compliance requirements, requesting a current compliance report from your service provider, filing a petition with the court or DMV (sometimes both), and attending a hearing if required. Expect to show completion of any DUI treatment programs, proof that fines are paid, and current insurance with your SR-22 on file.
End-of-term removal isn’t automatic either. You need formal authorization from whichever authority imposed the requirement. A court-ordered interlock usually needs a court order or clearance letter. A DMV condition needs the motor vehicle department to confirm eligibility and issue a license without the interlock restriction code. Some states mail an authorization form ahead of your removal date; others require a DMV visit first. Only after you have written authorization should you schedule a removal appointment. Removing the device without it counts as a violation.
If You Hold a Commercial Driver’s License
A DUI hits CDL holders harder than the interlock alone suggests. Under 49 U.S.C. § 31310, a first DUI in any vehicle, not just a commercial one, disqualifies you from operating a commercial motor vehicle for at least one year. If you were hauling hazardous materials at the time, the minimum jumps to three years.5Office of the Law Revision Counsel. 49 USC 31310 – Disqualifications
A second DUI results in lifetime disqualification from commercial driving. Federal regulations allow the possibility of reinstatement after 10 years under certain conditions, but that’s an option, not a guarantee, and many employers won’t hire a CDL holder with two DUI convictions regardless of reinstatement status.5Office of the Law Revision Counsel. 49 USC 31310 – Disqualifications The BAC threshold for commercial vehicles is 0.04, half the standard limit, so a CDL holder can face these consequences at alcohol levels well below what triggers a standard DUI.