Yes, an ignition interlock device (IID) can stop a car from starting, but only under specific conditions.
When Can an IID Prevent the Car from Starting?
An IID prevents the engine from starting if:
- Alcohol is Detected on the Driver’s Breath:
- If your breath alcohol concentration (BrAC) is above the preset legal limit (typically around 0.02%), the device will block the ignition system.
- You Refuse or Fail to Provide a Breath Sample:
- If no breath sample is given or the test is incomplete, the car won’t start.
- The Device Detects Tampering or Malfunctions:
- If the system identifies attempts to bypass, disconnect, or tamper with it, it may lock you out.
What the IID Cannot Do:
- It cannot turn off a running engine once the car has started.
- It does not control steering, braking, or acceleration.
- It does not shut the car down while driving, even if alcohol is detected during a rolling retest. It may log the event or trigger an alarm, but it won’t cut the engine (for safety reasons).
🔁 Example Scenario:
| Condition | Will the Car Start? |
|---|---|
| BrAC is below the limit | ✅ Yes |
| BrAC is above the limit | ❌ No |
| Breath test not provided | ❌ No |
| Device is tampered with | ❌ No |
| Rolling retest failed while driving | ✅ Yes (but logged) |
Are ignition interlock devices safe?
Yes, ignition interlock devices (IIDs) are generally safe—both in how they operate and in how they are used in vehicles. They are designed with safety and public protection in mind, especially to prevent impaired driving. Here’s a detailed look at their safety:
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