Ignition Interlock Devices (IID)

What Is an Ignition Interlock Device?

An ignition interlock device is a small electronic unit installed in your vehicle by a state-approved technician. It connects to your ignition system and requires a breath sample before the engine will start. If the device detects a breath-alcohol concentration (BrAC) above the preset limit — typically 0.02 to 0.025 — the vehicle will not start.

IIDs are designed to prevent impaired driving while allowing you to maintain driving privileges during your restriction period. The device logs every test result, and the data is reviewed at regular calibration appointments.

How Does an IID Work?

The IID operates in two modes: startup testing and rolling retesting.

Startup Test

Before starting your vehicle, you blow into the IID mouthpiece for several seconds. The device analyzes the breath sample for alcohol. If you pass (below the preset BrAC limit), the ignition unlocks and you can start the engine. If you fail, the vehicle will not start and the device logs the failed attempt.

Rolling Retests

While driving, the IID prompts random retests at intervals — typically every 15 to 45 minutes. You have a short window (usually a few minutes) to provide a sample. If you fail a rolling retest or miss the window:

• The engine does not shut off while driving — this is a safety feature.
• The device logs the event as a violation.
• Your horn may honk and lights may flash until you pull over and turn off the ignition.
• The violation is reported to your monitoring authority at your next calibration appointment.

Data Logging & Calibration

The IID records every breath test (pass and fail), every engine start, and any attempts to tamper with the device. At regular calibration appointments — usually every 30 to 60 days — a technician downloads the data, checks the device, and recalibrates the sensor. This data is reported to your state’s monitoring authority.

Who Needs an Ignition Interlock Device?

IID requirements vary by state, but common triggers include:

• First DUI/DWI conviction — Many states now require IID even for first offenses, especially if BAC was significantly above the legal limit.
• Repeat DUI/DWI convictions — Nearly all states mandate IID for second and subsequent offenses, often for longer periods.
• High BAC at arrest — Drivers arrested with a BAC well above the legal limit may face mandatory IID even on a first offense.
• Refusal to submit to a breath or blood test — Implied consent refusals trigger IID requirements in many states.
• DUI with a minor in the vehicle — Aggravated DUI charges involving child passengers often carry mandatory IID.
• Restricted license during suspension — Some states offer a restricted or hardship license that requires IID installation as a condition.

IID and SR22: How They Work Together

IID and SR22 serve different purposes and are independent legal requirements:

After a DUI conviction, you may need both. Neither satisfies the other — completing your IID period does not end your SR22 requirement, and maintaining SR22 does not exempt you from IID. The timelines may also differ: your IID period might end before your SR22 filing period, or vice versa.

In Florida and Virginia, DUI convictions require an FR44 filing instead of SR22, with higher liability limits — 100/300/50 in Florida and 100/200/50 in Virginia.

How Long Is an IID Required?

IID duration depends on your state, offense level, and court order:

• First DUI offense: Typically 6 to 12 months
• Second DUI offense: Typically 1 to 2 years
• Third or subsequent offense: 2 years or more, depending on the state
• High BAC or aggravating factors: Extended periods at the court’s discretion

Violations during the IID period — failed tests, missed calibration appointments, or tampering — can extend the required duration. Your court order or DMV reinstatement letter will specify the initial period.

IID Installation & Maintenance

IIDs must be installed and maintained by state-approved service providers. Here is what to expect:

1. Find an approved provider — Your state DMV website lists approved IID vendors and installation locations.
2. Installation appointment — A certified technician installs the device, which typically takes one to two hours. You receive training on how to use the device.
3. Regular calibration visits — Return to the service center every 30 to 60 days for data download, device inspection, and sensor recalibration.
4. Removal — Once your IID period is complete and approved by the court or DMV, the device is removed by the service provider. Do not remove it yourself — unauthorized removal is a violation.

Common IID Violations

The following events are logged and reported as violations. Any of them can extend your IID requirement:

• Failed breath test — Registering above the BrAC limit on a startup or rolling retest.
• Missed rolling retest — Not providing a sample within the allotted window during a driving retest prompt.
• Tampering or circumvention — Any attempt to bypass, disconnect, or physically alter the device.
• Missed calibration appointment — Failing to bring the vehicle in for a scheduled service visit.
• Driving without IID — Operating a vehicle that does not have the required IID installed.
• Having someone else blow — Using another person to provide the breath sample (most modern devices include a camera).

Frequently Asked Questions