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Drunken driving is considered one of the worst offenses in the U.S. When you have a driving under the influence (DUI) conviction on record, you’ll have to deal with some significant changes in life. Apart from paying hefty fines and attending court hearings, you may also be required to install a vehicle breathalyzer or an ignition interlock device (IID) in your vehicle.

If you don’t know what an ignition interlock device is, here is a general overview of how it works, how to use it correctly and how test data is logged.

What is an Ignition Interlock Device?

This is a device that prevents a driver from starting a vehicle if they have been drinking. Ignition interlock devices work like breathalyzers, measuring the alcohol level in your blood system. If the amount of alcohol in your blood exceeds a pre-programmed level, then the interlock device temporarily locks your vehicle’s ignition.

No one wants to have an interlock device installed in their car, but with a DUI conviction, you have no option but to comply. You can choose the type of breathalyzer you want while considering factors like the interlock device cost, features and reliability.

How Does it Work?

Ignition interlock devices prevent drunk drivers from driving a vehicle. The device is simply connected to your vehicle with a preset level for blood alcohol concentration that varies from state to state. If you blow into the interlock device when you’re over the set limit, your vehicle will not start.

All interlock devices installed must meet and exceed the local and state regulations as well as the National Traffic Safety Administration (NHTSA) standards. An interlock device is installed for your own good, ensuring that there’s no alcohol in your system before you start your vehicle.

The Initial Test

If you have an interlock device installed in your vehicle, you’ll have to take an initial test. You have to breathe into the device, and if the test sample is good, your vehicle will start. If alcohol is detected in your system, you’ll have to wait a little bit, usually a few minutes before testing again. If subsequent tests fail, you’ll have to wait for longer periods.

Rolling Re-Test

Most states have in place regulations that require all drivers who have interlock devices installed in their vehicles to conduct random re-tests on the road. The device will beep at certain times when you’re driving, signaling you to perform a breath sample.

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It’s important to understand that if alcohol is detected, the interlock device will not turn off the engine while the vehicle is moving. Normally, the device will signal you to stop the vehicle by flashing the lights or blowing the horn. The rolling re-test is done to ensure you don’t consume alcohol after performing the initial test.

How is Data Logged? 

All your breath samples are logged and sent to the specific authority that ordered the interlock device to be installed in your vehicle. This could be a local court, the Department of Motor Vehicles (DMV) in your state or probation rules. Depending on your state, logged data is usually sent immediately, wirelessly or even once each month during your regular service appointments.


Most U.S. states now use ignition interlock devices as an effective alternative to revoking driving privileges for drivers charged with DUI. They play an important role in preventing drunk driving today while also giving those convicted of DUI an opportunity to perform normal tasks like driving to work and attending school.

In fact, there has been an increase in ignition interlock device use, with the devices reducing repeat DUI offenses by about 70% when they are installed.


  1. These are really useful information to know about In-Car Breathalyzers. I agree that, apart from paying fines and attending court hearings, it is important to install an ignition interlock device. Thanks for sharing, appreciate your post..!!

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