An ignition interlock device is a piece of equipment installed into your vehicle that measures any amount of alcohol on your breath. If you are convicted of a DUI/DWI, a court can order you to have one installed to monitor your alcohol consumption. It is connected to your starter and in order to start your car, you have to blow into the device first.

The way you blow into the device can vary, based on the provider you’ve chosen and their specific ignition interlock device. The most common is the blowing and humming pattern. Having you hum as you blow into the device helps the device recognize it is a person blowing into it and not canned air, or some other means of blowing air.

Another method some providers use is a blow and inhale pattern. This method may be seen as being potentially unhygienic, since you are basically re-inhaling everything you just blew out.

When you blow into your ignition interlock device, you can expect one of four common outcomes. The first, which is the one you always hope to have, is a pass. This means you either have zero alcohol on your breath or you are significantly below your allowed limit. The second outcome you might see is a warning, which indicates you are very close to reaching your allowed limit and need to stop drinking, or your car will not continue to start. The third outcome is a fail. This means you are at your allowed limit or have exceeded it and this will prevent your vehicle from starting. Every time you receive a fail result, you will also incur a violation. This is logged and reported to your monitoring authority. A certain number of violations will have legal ramifications and/or additional jail time.

While an ignition interlock device is installed in your vehicle, there are two test types you will be asked to perform, an initial test and a rolling test. The initial test happens when you blow into your ignition interlock device to get your car started. You pass the test, your vehicle starts. You fail the test, your vehicle does not start. A rolling re-test occurs after you’ve already begun driving. You will be asked to blow into your ignition interlock device and you will have a certain number of minutes to perform the re-test. If you ignore the re-test request, you will receive a violation.

Now that you know the basics of what an ignition interlock device is and how it works, the next step is to find one that fits your needs. You will never be able to purchase an ignition interlock device. They are only available for leasing on a monthly basis, or through a long-term contract. You can read here about how to lease your device, the pros and cons of a monthly vs. long-term contract, and find the top ignition interlock providers available in your area.