What is an ignition interlock device?
An ignition interlock device (IID) is a breath alcohol analyzer wired into a vehicle's starting system. It sits within reach of the driver's seat, usually on a cord near the dashboard. Before the engine will start, the driver blows into the mouthpiece. The device measures the alcohol concentration in the breath sample, and if the reading is above the preset limit, the vehicle will not start.
Interlocks are used across the United States as a way to let people drive legally after an alcohol-related offense while reducing the risk of impaired driving. The device does not punish the driver for having it. It simply verifies sobriety each time the vehicle is used.
How the device works day to day
- Initial test. Blow into the device before starting the engine. A clean sample lets the vehicle start normally.
- Rolling retests. While driving, the device periodically asks for another sample. You get several minutes of warning, and you can provide the sample while the vehicle is in motion or pull over safely first. Rolling retests confirm that the person who started the car is still the one driving sober.
- Data logging. The device records test results, missed tests, and attempts to tamper with the unit. This log is downloaded at regular service visits and reported to the monitoring authority.
- Calibration. Interlocks need periodic calibration at a service center to stay accurate. Skipping a calibration appointment can put the device into a lockout state.
Common misconceptions
An interlock will not shut off a moving vehicle. If a rolling retest is failed or missed, the device records the event and may trigger alarms until the vehicle is turned off, but it never cuts the engine in traffic. The device also does not read anything other than breath alcohol. It does not detect drugs, and it does not track location on its own.
Modern devices include features that make daily use easier, such as quick warm-up, simple breath patterns, and clear indicator lights. Most drivers report that using the device becomes routine within the first week or two.
Next, read about when Florida requires an interlock or jump to how installation works.