1. Before Driving

Before the car can start, the ignition interlock device must boot up and check for readiness.

What happens:

• The driver turns the key or presses the start button

• The IID powers on

• The screen shows a message such as “Blow to Start”

• The driver inserts the mouthpiece if required

No breath sample = no engine start.

2. Initial Breath Test

The device will prompt the driver for a breath sample.

How it works:

• The driver blows into the mouthpiece for several seconds

• Some devices require a specific pattern like blow–inhale–blow

• The fuel-cell alcohol sensor analyzes breath alcohol concentration (BrAC)

Results:

• If BrAC is below the state limit → the ignition is enabled

• If BrAC is above the limit → the car stays locked out

3. Start Allowed or Blocked

After analyzing the breath sample, the IID decides whether to let the vehicle start.

If the test is clean:

• The IID sends a signal to the ignition system

• The starter is unlocked

• The driver can start the vehicle normally

If the test is failed:

• The car will not start

• The device may enter a short lockout period (a few minutes)

• The driver may be prompted for another test after the lockout expires

Violations are recorded even if the car never starts.

4. Rolling Retests While Driving

Once the car is running, the IID continues monitoring sobriety through rolling retests.

What happens:

• The device beeps randomly and asks for another breath sample

• The driver has a time window (usually 5–10 minutes) to safely provide the sample

• The car will NOT shut off during a failed or missed rolling retest

However:

• Failed or skipped retests are logged

• Multiple violations may trigger a service lockout

• A service lockout prevents the vehicle from starting later until the device is serviced

Rolling retests ensure ongoing compliance, not just a clean test at startup.

5. Data Logging and Reporting

Every event is securely recorded inside the device.

Data stored:

• Passed breath tests

• Failed tests

• BrAC levels

• Missed or refused retests

• Tamper attempts

• Power loss events

• Lockouts

• Date and time stamps

Depending on the device and state:

• Data is uploaded automatically via a cellular connection

• Or downloaded during monthly service appointments

Authorities review this data to determine compliance with court or DMV requirements.

Why Understanding This Matters

Knowing how an ignition interlock device works helps drivers avoid violations, understand the system's expectations, and complete their program with fewer issues. The process may seem intimidating at first, but once broken down step by step, it becomes predictable and manageable.

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