Ignition interlock devices have two main jobs:
Prevent somebody from starting their car while intoxicated
Guarantee continued sobriety from the driver throughout their time behind the wheel
Let’s look at how the devices work to accomplish each of these goals.
Preventing a driver from starting the vehicle while intoxicated
Anybody with an ignition interlock device installed in their vehicle will be required to provide a breath sample into the mouthpiece of the device before they are able to start their vehicle.
State certified ignition interlock devices use a fuel cell technology to measure the amount of alcohol on the user’s breath. If the breath sample detects alcohol at or above the limit set by the state (usually 0.02), the car will not start.
If the breath sample returns a breath alcohol concentration (BrAC) below that set limit, the driver will be able to insert their key into the ignition and start their vehicle.
Each state has individual ignition interlock device laws and regulations that determine what happens if you provide a failing breath sample.
Some states allow you to try again after waiting a short period of time but may lock you out after so many failed samples. More about lockouts later on in the guide.
Other states allow you to continue blowing into the device until you’ve provided a passing breath sample and can start your car.
Your ignition interlock provider, attorney, court or Motor Vehicle Department can walk you through the requirements in your state so there aren’t any surprises.
Of course, the best way to get through an interlock requirement is to refrain from trying to drive after consuming any alcohol.
You will have 4-6 minutes to complete a random retest
Continuous sobriety while the vehicle is running
Once your vehicle is started, an ignition interlock device will require you to continue providing breath samples throughout the duration of your trip.
Simply put, this ensures that the driver doesn’t just have a sober person start their vehicle for them so they could continue driving after drinking.
These continued tests, often referred to as random retests, are required by your state and all ignition interlock providers must abide by state laws requiring them.
Most ignition interlock providers give the driver 4-6 minutes to complete a retest once prompted. This allows the driver to pull over to the side of the road if needed or take extra precautionary measures if driving in heavy traffic.
Are retests safe?
Retests have proven to be safe and effective at separating drinking from driving and if done safely, can be executed without any issues. Your device will beep when a retest is required. At this time, you’ll simply provide a breath sample into the mouthpiece and can continue driving.
If you provide a breath sample with a BrAC above the limit set by your state, your vehicle will signal you to pull over and turn your car off. As with most things related to ignition interlock devices, the specifics differ by state.
Some states will require your horn to beep or your lights to flash after a failed retest until you turn your vehicle off. In NO situation will the ignition interlock device be able to actually turn your car off, though. Once your vehicle has been started, no ignition interlock device is able to turn it off.