How Sensitive Is an Ignition Interlock Device?

If you’re reading this, you probably already know the basics of how an ignition interlock device (IID) works. The IID is connected to your vehicle’s starter. Each time you want to start the car, you have to blow into the handheld device to submit a breath sample. If the device detects a blood alcohol content (BAC) above what the state allows (generally 0.02%), the device locks you out. Many people can have a BAC of 0.02% after one drink. If the device finds that you have submitted a clean breath sample, you can start the car. Pretty simple, really.

But exactly how sensitive is an ignition interlock device? Highly sensitive. The National Highway Transportation Safety Administration (NHTSA) model specifications for breath alcohol ignition interlock devices lay it all out. Warning: Some of this gets a little technical.

Sensor Technology

Most ignition interlock devices in use today use alcohol fuel cell sensor technology. The ignition interlock device industry pushed the NHTSA to require alcohol-specific sensor technology. Non- alcohol-specific devices are not as accurate. Alcohol fuel sensor technology enables the devices to distinguish between alcohol and acetone, or cigarette smoke, for example.

Breath Sample Volume and Minimum Flow Rate

Breath sample volume refers to how much air you blow into the device. Flow rate refers to the intensity of the blow. Currently, the breath sample volume is set at 1.2 liters (L). The flow rate is set at 0.3L/second. In this way, IIDs are standardized for how long you have to blow, and how hard you have to blow for the breath sample to be acceptable to the ignition interlock device.

The devices will not accept a volume of 1.0 liter but will accept a volume up to 1.5 L. And for flow rate, they will not accept a flow rate as low as 0.1 L/sec but will allow the vehicle to start with a clean sample at 0.7 L/sec flow rate. When we say the “devices will not accept” that essentially means that you blew an invalid sample, and the device will ask you to try again.

Precision and Accuracy

Before ignition interlock devices make it to market, they must undergo rigorous testing. They must measure BAC accurately and must be precise, as in they must repeatedly give the same results for the same BAC.

The NHTSA guidelines state:

“IIDs must experience no ignition locks at 0.000 g/dL (grams of alcohol/210 liters of air); not more than one ignition lock in 20 trials at 0.008 g/dL; and not more than one ignition unlock in 20 trials at 0.032 g/dL. (75 Fed. Reg. 61828.) “

So the bottom line is, an ignition interlock device is a very sensitive piece of equipment, designed to detect even the slightest amount of alcohol on your breath. You should know that in many states if the IID detects even the smallest amount of alcohol on your breath, it records that, and gives you a warning. You may still be allowed to drive if the amount is under the cutoff, but you may face consequences. Your state ignition interlock device program rules and requirements will spell it all out for you.

Fast and Affordable Ignition Interlock Device Installation

ALCOLOCK offers fast and affordable ignition interlock device installation at service locations across the country. If you need to get an IID installed, call one of our service centers directly, or call ALCOLOCK at (866) 700-9300 to set up your appointment. You can speed up the process if you have your DMV/DOT paperwork with you. We’ll need some of that information.

On the day of your IID installation, you’ll need to have someone drive you and your vehicle to your appointment. If someone else will be driving the car while the IID is installed, it would make sense for them to be the person to drive you. We’ll train you and any other driver how to use the IID, and what all of the sounds and messages mean. You will also get an owner’s manual to keep in the car for the duration of your restricted driving program. Once we’re done with the installation and training session, you’re free to drive.

Scheduling Your First Service Visit

Before you leave your installation appointment, your technician will schedule your first service visit. Every state requires these service visits, usually every 30 days. We can schedule your visit for a day and time that is convenient for you. At each service visit, the technician will transmit all of the information the device has recorded to your monitoring agency, which is usually the DMV/DOT.

The technician will also recalibrate the device as needed, and then schedule your next appointment. And don’t worry, the device actually reminds you of an upcoming appointment!

At ALCOLOCK, our goal is to get you back on the road quickly. We look forward to serving you!

Skip to toolbar