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July 4, 2024

What Does an Ignition Interlock Device Detect?

Ignition interlock devices, also known as car breathalyzers, are required for DUI offenders who are in a restricted driving program in many states. These devices require a driver to blow into the device before starting their vehicle. The device analyzes the breath sample for traces of alcohol and sends the data to their ignition system. However, the IID is not foolproof and there are many misconceptions about how the device works. This article addresses some of the common questions and myths about the ignition interlock device.

Myth #1 - It’s possible to trick the device.

An ignition interlock device uses fuel cell technology to detect the presence of alcohol in the breath of a person who is trying to drive. When a person drinks alcohol, it is absorbed into the bloodstream and carried to every organ in their body including the heart, lungs, liver, and stomach. Once the alcohol is in these organs, it is metabolised or broken down. This process can take up to several hours depending on how much alcohol was consumed, the type of alcohol (liquor, beer, wine), and whether it was eaten or not. The result is that there can still be traces of alcohol in the body even after people feel completely alert and functioning, which can result in them failing a breath test on an interlock device.

When a person breathes into the ignition interlock device, it measures the concentration of alcohol in their blood and compares that with the preset limit set by their court order or state law. When a person’s BAC is above the set limit, the device will sound an alarm and shut off the engine. The interlock device will then require a new breath sample and continue requesting retests until it is satisfied that the driver’s BAC is below the threshold.

The retests that the device requests are known as rolling tests and can be taken any time after a person has blown into the device. This can include during a stop at the gas station or while the vehicle is in motion. If a rolling test indicates that the user’s BAC is above the preset limit, the device will log a “fail” report for the offender and notify their monitoring agency in near real-time.

Myth #2 - Ignition interlocks can detect the use of marijuana.

It’s important to understand that the ignition interlock device can only check your Breath-Alcohol Content and cannot detect the presence of weed (also known as marijuana, cannabis, or pot). This is because the IID only measures ethanol and not vapors from smoked marijuana. As such, using weed while you’re in a DUI restriction program could lead to a revocation of your IID installation requirements and serious legal penalties. Our Boise DUI team stays updated on the latest nuances of ignition interlocks so we can best advise our clients on how to navigate these strict regulations.