Learn How Interlock Devices Work After License Suspension

What an Interlock Device Actually Does and Why Courts Order Them

An ignition interlock device (IID) is a breathalyzer installed directly into your vehicle's dashboard. When you sit down to start your car, the device requires you to blow into a tube before the engine will turn on. The machine measures the alcohol content in your breath and either allows the engine to start or prevents it from starting based on what it detects. This isn't a choice—once a court orders one, it becomes a legal requirement for operating any vehicle during your suspension period.

Learn About Filing for SSDI Online →

Courts order these devices as an alternative or supplement to a complete license suspension. Rather than losing all driving privileges, many people can continue driving to work, school, or medical appointments—but only if they pass the breath test each time. The goal isn't punishment alone; it's prevention. The device physically stops an impaired person from driving, regardless of their intentions or judgment at that moment.

The technology has existed since the 1990s, but it's become far more common in the last 15 years. States use them differently. Some require them for first-time DUI offenders; others only mandate them for repeat offenders or cases involving high blood alcohol content. The specifics depend entirely on your state's laws and the judge's decision in your case.

Here's what matters to understand: this isn't a monitoring device that reports your location or sends data to police about where you drive. It's purely a mechanical barrier to starting the car. You can still be pulled over for traffic violations, and you can still face consequences if you tamper with the device—but the IID itself doesn't track you or limit where you go once the engine starts.

Practical takeaway: An IID is a safety interlock on your engine's ignition system, not a surveillance tool. It requires a breath sample before each drive and won't let the car start if alcohol is detected above the legal threshold (typically 0.02% BAC).

How the Installation Process Works and What to Expect

After a court orders an interlock device, you'll receive notification about which certified vendor you must use. In most states, you don't get to choose—the court assigns an approved provider. You'll need to contact that vendor, schedule an appointment, and bring your vehicle to their installation location. This typically happens within a few weeks of the court order, though some jurisdictions give you 30 days or more to complete it.

Learn How to Install an EZ Tag on Your Vehicle →

The actual installation takes 1-2 hours. A technician will run wiring from the device through your dashboard to your steering column, connecting it to your ignition system. They'll install the breath tube (usually mounted near the steering wheel), explain how to use it, and run several test breaths to make sure it's calibrated correctly. The device uses a standard tube—similar to what you'd blow into at a police station, but slightly different in design.

Installation costs money. Depending on your state and vendor, you can expect to pay anywhere from $100 to $400 for installation alone. Some vendors charge less for installation if you're signing a longer-term contract. Then there are monthly monitoring fees—typically $60 to $100 per month—which vary based on your location and whether your device has GPS capability (more on that later).

You'll also need to get your vehicle inspected by the vendor to confirm the device is working before you can use it for driving. Some vendors do a quick inspection during installation; others schedule a separate appointment. You must complete this inspection before driving, not after.

One important detail: the device gets installed in one specific vehicle. If you drive multiple cars, you'd need an interlock in each one—or you can only legally drive the vehicle with the installed device. Some people arrange to borrow a family member's vehicle with an interlock instead of putting one in multiple cars.

Practical takeaway: Plan for 1-2 hours at the installation appointment, bring your vehicle keys, budget for installation costs ($100-$400) plus monthly fees ($60-$100), and understand that you can only drive vehicles with an installed and inspected interlock device.

The Daily Breath-Test Routine: What Happens Every Time You Drive

Every single time you want to start your vehicle, you blow into the tube. You'll need to take a deep breath and blow steadily for about 5-7 seconds. The device analyzes your breath alcohol content and gives you immediate feedback. If your BAC is below the legal threshold set by your state (usually 0.02%, which is lower than the standard 0.08% DUI limit), the light turns green, a tone sounds, and you can start your engine.

How to Charge Your Apple Magic Mouse →

If you blow over the limit, the device won't start your car. The light turns red, there's typically a buzzer or horn, and you're locked out of the ignition. You cannot force-start the vehicle or bypass this. You'll need to wait a few minutes, then try again. Most devices give you 3-4 attempts within a 24-hour period before requiring a reset or technician intervention.

This isn't a one-time test at the beginning of the day. Some devices require what's called a "rolling retest"—a random breath test while you're already driving. Usually, this happens 5-15 minutes after you started the car and then at random intervals. If you're asked for a rolling retest, you have a grace period (typically 5-10 minutes) to pull over safely and provide the sample. You blow into the tube while parked. If you pass, you're fine. If you fail or don't provide a sample within the grace period, the device logs it as a violation.

Here's a realistic scenario: You drive to work in the morning, pass the initial test. An hour later, while you're at your desk, the device sends a signal (if it's connected via Bluetooth to your phone). You have maybe 10 minutes to get back to your car and provide the sample. If you miss this window, it's recorded as a missed test. Three missed tests or one failed test, and your interlock provider typically alerts you to schedule a service appointment or sends a report to the court.

The device keeps a digital log of every test—passed, failed, missed, tampered with, or whatever else happens. This data is downloaded during monthly monitoring appointments or, in newer devices, transmitted wirelessly. Your probation officer or the court can review this record.

Practical takeaway: Plan to blow into the tube before starting your vehicle every time. Expect random retests while driving. Failed tests, missed tests, or attempts to tamper with the device are all documented and can trigger court involvement or extension of the interlock requirement.

Understanding Device Settings, Lockout Periods, and Violations

Each state sets its own BAC threshold for interlock devices. Most use 0.02%, which is one-quarter of the legal driving limit. This is intentionally low—the idea is that even one drink could trigger a lockout. Some states use 0.04% for repeat offenders, and a few use 0.05%. Your device is programmed with your state's threshold before installation.

Learn About Paying Your Trash Bill Online →

When you fail a breath test, the device doesn't just reject your start—it enters a lockout period. During this time, you cannot start the vehicle. The typical lockout is 15-30 minutes, though this varies. The device usually has a countdown timer or display showing when you can try again. If you fail again after the lockout expires, another lockout is triggered, often extending longer each time within a 24-hour period.

If you have multiple failures or lockouts in a short period, the device may require a service appointment before it will reset. Some devices lock you out for 24 hours after, say, five failures in a day. You'd need to contact your vendor and possibly visit their office for a technician reset. They'll review the data, charge you a reset fee (usually $50-$150), and ask questions about what happened.

Violations fall into categories: breath test failures (you blew over the limit), missed tests (rolling retest you didn't complete in time), tampering (removing the device, blocking the tube, eating something to mask breath), and other device malfunctions. Your vendor and the court track these. If you have too many violations, you might face license suspension extension, increased monitoring, jail time, or other penalties depending on your state and the original offense.

Some devices have features like alcohol detection that prevents you from even getting a breath-test opportunity if