A blow and go ignition interlock device is a breathalyzer wired into your car’s ignition that keeps the engine from starting until you provide a breath sample below a set alcohol limit, usually 0.02 g/dL, and then asks for more samples at random intervals while you drive. Courts and motor vehicle agencies order these units after alcohol-related driving offenses, and around 30 states plus the District of Columbia require one even after a first DUI conviction.1National Conference of State Legislatures. State Ignition Interlock Laws The mechanics are simple once you see the sequence. The consequences of fumbling that sequence are not.
Starting the Car
When you turn the key or press the start button, the handheld unit powers on and prompts you for a breath sample. Most devices want a specific blow pattern, typically a steady exhale for several seconds and sometimes a hum, so the sample clearly comes from a person rather than a pump or balloon. In cold weather, the unit can take up to three minutes to warm up, so plan for that in your morning routine.
Blow under the programmed limit and the ignition unlocks. The federal model specification sets that cutoff at 0.02 g/dL, and most states use that number or something close.2Federal Register. Model Specifications for Breath Alcohol Ignition Interlock Devices Blow over it and the device locks you out. The first lockout is usually about five minutes. Fail again and the wait typically stretches to 30 minutes. Keep failing and some units enter a permanent lockout that only a certified technician can clear.
The sensor inside is specific to ethanol, so it won’t react to things like the acetone on the breath of someone on a low-carb diet. It’s the same kind of sensor law enforcement breathalyzers use, built tougher for daily vehicle life.
Rolling Retests While You Drive
Getting the engine started is not the end of it. Once you’re moving, the device will ask for more breath samples at random points. Federal specifications require the first of these rolling retests within five to seven minutes of a successful start, with more at random intervals after that.2Federal Register. Model Specifications for Breath Alcohol Ignition Interlock Devices You generally get about six minutes from the alert to provide a sample, which is enough time to pull over safely.
The device will not shut the engine off mid-drive. That would be dangerous, and it isn’t how the unit is built to behave. What happens instead: a failed or missed retest is stored as a violation, and in most configurations the unit will honk the horn or flash the lights until you either give a clean sample or turn the ignition off. Every failed, missed, or skipped test lives in the data log and gets reported to your monitoring authority at your next service visit.
Avoiding False Positives
Registering a positive when you haven’t been drinking happens more often than most people expect. Alcohol-based mouthwash is the biggest offender. You spit it out, but residual alcohol in your mouth can take 15 minutes or more to clear. Switch to an alcohol-free mouthwash for the duration of your program, or wait at least 15 minutes before blowing. Breath sprays containing alcohol carry the same risk.
Other everyday items that can produce a trace reading:
- Kombucha and other fermented drinks, including versions labeled non-alcoholic, which still contain trace alcohol from fermentation.
- Vanilla extract and cooking wines, which are high-proof and linger in the mouth if you taste while cooking.
- Sugar-free gum and diet drinks containing sugar alcohols like xylitol and erythritol, which can occasionally trigger a reading.
- Hand sanitizer or cologne sprayed near the device just before a test, which can put ethanol vapor into the sample.
The universal fix is to rinse your mouth with water and wait a few minutes before blowing. If a reading comes back positive and you haven’t been drinking, wait for the lockout to expire, rinse, and test again. The initial failure still logs, but a clean follow-up gives your monitoring authority context that points to a false positive rather than actual impairment.
How the Device Knows It’s You
Modern units are built to detect whether a real person is on the mouthpiece. The sensor analyzes the sample for temperature, humidity, and CO2 consistent with human breath. The blow-and-hum pattern most devices require is difficult to fake mechanically.
A growing number of states also require a camera in or near the unit. It automatically photographs whoever is blowing at startup, during rolling retests, and any time a violation occurs. Those images travel to your monitoring authority along with the breath data. If someone blows for you, the photos make that obvious. Every state that defines circumvention treats a substitute blower as a violation, and the consequences fall on both people involved.
What a Violation Costs
Violations sort into a few categories: failed startup tests, failed or missed rolling retests, missed service appointments, and tampering or circumvention. What happens next depends on your state and the severity of what the log shows.
A single failed test followed a few minutes later by a clean one, the pattern you’d expect from mouthwash or food, may not draw a heavy penalty, but it still shows up on your record. Repeated failed tests, especially at high readings, are handled differently. Common consequences include an extension of your IID requirement, additional fines, suspension of your restricted license, or a probation violation hearing that can result in jail time.
Tampering is where the legal exposure jumps. That covers disconnecting or disabling the unit, having someone else blow, driving a car without an IID when you’re required to have one, or physically altering the device. Most states treat tampering as a misdemeanor with potential jail time up to six months to one year and fines that can reach $5,000 depending on the jurisdiction.3National Conference of State Legislatures. Penalties for Tampering with or Circumventing Ignition Interlock Devices Beyond the criminal charge, your license is usually revoked and the IID requirement extended or restarted.
Installation, Costs, and Service Visits
Only a certified service provider can install the device. A technician wires it into your vehicle’s ignition and electrical system, calibrates it, and walks you through operation. Installation usually runs one to two hours. You lease the unit rather than buy it.
Expect roughly $70 to $150 for installation, then $50 to $120 per month in lease and monitoring fees, plus a removal fee at the end. A one-year program often totals $1,000 to $1,500 or more. Some states offer reduced-cost programs or hardship waivers, so it’s worth asking your service provider or monitoring authority.
Service appointments are mandatory, typically every 30 to 60 days depending on the state. At each visit the technician downloads the data log, recalibrates the sensor, and inspects for tampering. Every startup attempt, every rolling retest, every violation, all of it goes to your monitoring authority, which may be the court, a probation officer, or the DMV. Miss an appointment and that’s its own violation, and the device can lock out.
How Long You’ll Have It
The length of the requirement depends on the offense and your state’s law. A first DUI without injuries typically runs six months to a year. Second and third offenses usually run one to three years. Cases involving injuries, fatalities, or very high blood alcohol readings can push it to three or four years. Violations during the program can extend the clock; a failed rolling retest in month eleven could add months to the total.
Courts sometimes offer the IID as an alternative to a full license suspension. You get a restricted or hardship license that lets you drive to work, school, medical appointments, and IID service visits, but only in the interlock-equipped vehicle. For most people the tradeoff is worth it, because a full suspension means no legal driving at all.
Getting the Device Removed
Removal doesn’t happen automatically the day your mandated period ends. Most states use compliance-based removal, which requires a clean record for a set number of consecutive months, often the final three to six of your program, with no alcohol-related violations, no missed retests, and no skipped service appointments. A slip late in the term can push the finish line back.
Once you’ve met the time and compliance requirements, your monitoring authority authorizes removal, you obtain the paperwork confirming eligibility, and you schedule an appointment with your certified service provider. The technician takes the device out, performs a final data download, and closes your account. There is usually a de-installation fee.
Pulling the device off yourself before you’re authorized is one of the worst moves available. Depending on the state, early removal without approval can restart the entire IID requirement from day one or tack months onto your program, on top of whatever criminal penalties your state imposes for circumvention.