How Do Ignition Interlocks Work?

If you’ve been ordered to install an ignition interlock in your vehicle or you just want to take precautions, you may have a few questions about this device. Given the seriousness of what it’s tasked to do, it’s understandable that a big question you may have is how this machine actually works.

What Is an Ignition Interlock?

First, let’s establish what an interlock is. The main component of the device is usually just a bit larger than your cell phone. Most people have theirs attached to the dashboard of their vehicle by Velcro. There’s no reason for it to be permanently installed.

A device then runs from the cord under the steering column, through the open cavity and all the way to your ignition.

The reason it does this is because an ignition interlock device is tasked with the job of registering your BAC (Blood Alcohol Content) and either turning the ignition on or preventing it from doing so. These devices were created to ensure that no one drives a vehicle when they could be a danger to themselves or others.

Depending on the situation, your interlock may allow you to drive so long as you blow below 0.08%, the legal limit in all 50 states or some other number, like a 0.02%. Some people though—either because of the courts or their own preference—will have a device that won’t allow them to drive if they have any traces of alcohol on their breath.

How Does the Machine Work?

When someone has an ignition interlock installed gets into their car, they must first blow into the device before they can start the vehicle. An ignition interlock system has a small plastic mouthpiece attached to the handheld portion. This piece can be replaced as necessary, to guarantee sanitation, or simply removed and washed.

Once the driver blows a full breath into the machine, it will draw the air into a fuel cell sensor. Absolutely any alcohol present will set off a reaction with this sensor, which in turn will create water and electricity.

The machine uses the combination of water and electricity to create a reading of the driver’s BAC.

That cord that runs from your device to the ignition is a relay that remains open until it’s told to do otherwise. It’s no different than the ignition line that begins with your key. When you turn the key, the relay closes, allowing a current to travel to your ignition and bring it to life.

With an ignition interlock device installed, the only way that relay is now going to close is if your breath is measured and shows that you have an acceptable BAC. Otherwise, it will keep the relay open and current can’t travel to wake up your ignition. It will also make you aware of its findings.

Again, installation of these devices is temporary. Even the connection to your ignition is noninvasive, meaning that when you no longer want the device or don’t need it anymore, a mechanic can remove it without issue.

Given the sophistication of these machines, you can rest assured they will produce accurate readings every time. Many have tried to trick or tamper with ignition interlock systems, but they’re simply too sophisticated.