Jeffrey Johnson is a legal writer with a focus on personal injury. He has worked on personal injury and sovereign immunity litigation in addition to experience in family, estate, and criminal law. He earned a J.D. from the University of Baltimore and has worked in legal offices and non-profits in Maryland, Texas, and North Carolina. He has also earned an MFA in screenwriting from Chapman Univer...

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Laura Walker graduated college with a BS in Criminal Justice with a minor in Political Science. She married her husband and began working in the family insurance business in 2005. She became a licensed agent and wrote P&C business focusing on personal lines insurance. Laura serviced existing business and wrote new business. She now uses her insurance background to help educate drivers about...

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Reviewed by Laura Walker
Licensed Agent for 10 Years

UPDATED: Apr 23, 2019

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An ignition interlock device (IID) is a machine that is attached to your car’s dashboard and tests your breath for alcohol content. These devices are used to prevent anyone under the influence from operating a motor vehicle.

Most IIDs are small and linked to the car by a tether which plugs in to some power source, such as a lighter, and have a small pipe at the end into which the driver blows.

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Despite popular belief, the IID does not simply “turn off” the engine of a car. Some models are made to keep the car from starting if the blood alcohol content (BAC) of the driver exceeds a certain level.

However, the IID often requires random breath tests while driving, as well, and in this case the car will not shut off automatically, although an alarm may sound and lights may flash. The IID requires random samples during a drive for two reasons.

First, a driver could have someone else blow into the device, resulting in a “clean” test that allows the engine to start, even if the driver has been drinking. Second, the driver could be consuming alcohol while driving, even if he or she was initially sober.

How does an Ignition Interlock Device Work?

IIDs have a fuel cell that senses ethanol, the primary alcohol in beverages. The fuel cell uses a catalytic surface of platinum to create an electrical current. The current is then converted into a blood alcohol reading.

A few models use infrared spectroscopy, which measures the reflected light of a substance and translates it into specific chemical components, but these models are very expensive and are not often used for dashboard-mounted IIDs.

An IID must be maintained to give accurate readings. Many companies offer the product and the monthly servicing for a fee.

After the initial installation costs of the device, the monthly fee for maintenance averages $75.00. IIDs are often installed as the result of a court order.

Many states allow courts to mandate the installation of IIDs for drivers after a DUI conviction. Some states allow this after the first DUI offense; most allow it after multiple offenses.

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Who pays for an Ignition Interlock Device?

The costs of installing and maintaining the device are borne by the offender. If the person convicted of DUI agrees to install and maintain the IID, many courts allow the driver’s license to be reinstated on a probationary basis. This is often called a “restricted license.”

If the driver fails to prove that the IID is installed and working properly, the state may revoke the license and charge the offender a fine.

Many courts require periodic readouts from the IID. IIDs are programmed to store all information about usage and generate a printed report of activity, so anyone who has blown into the device is recorded.

For this reason, it is never a good idea to allow anyone else to drive your car if you have an IID in place. It is also not a good idea to allow someone else to blow into the device for you, as a string of variable readings may alert authorities to misuse of the product.

Who provides the Ignition Interlock Device?

The National Highway Traffic Safety Administration maintains a list of approved providers for IIDs. In order to be listed, the provider must meet minimum calibration standards for the device, as well as conform to the requirements for specific readings and reporting.

The use of IIDs has been debated in the United States and other countries. Proponents feel that these devices will decrease drunk driving deaths by making it clear to drivers what their BAC is before they start the ignition.

In many cases, people convicted of DUI claim they had no idea how drunk they were; an IID would prevent that situation.

Unfortunately, as the detractors point out, IIDs are usually installed only after a DUI conviction.

There is support for laws which would require car manufacturers to install IIDs in every car produced, but some groups argue that this violates the right to free enjoyment and needlessly punishes the majority of people who do not have DUI convictions and do not drive drunk.

Mothers Against Drunk Drivers (MADD) has launched a public campaign to encourage state legislatures to install these devices in any driver’s vehicle upon the first DUI conviction, but many states so far are refraining from using them except in extreme cases.

Detractors argue that the mandating of IIDs places undue financial burden on the driver, who is already likely experiencing heavy fines and loss of transportation, plus any damages caused by his or her driving.

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