Criminal Law

What Is an Ignition Interlock Device (IID)?

By John McCurley, Attorney
Read about how ignition interlock devices (IIDs) work, and when the law requires DUI offenders to install them.

In many states, motorists who get convicted of a DUI have to install ignition interlock devices (IIDs) on their vehicles. An IID is essentially a breathalyzer that’s wired to the car’s ignition system. IIDs are designed to prevent a car from starting if the driver has had anything to drink.

How IIDs Work

Start-up tests. With an IID installed, a car won’t start unless someone blows into a tube with an alcohol-free breath. But how does the machine know it’s the driver and not a passenger blowing into the tube? It doesn’t. If anyone—not just the driver—blows into the tube with a clean breath, the car will start. However, it’s typically a crime for a driver to have someone else blow into an IID. (See Cal. Veh. Code § 23247 (2016).)

Rolling tests. To make it more difficult for drivers to evade detection, most IIDs require “rolling” samples every so often after the car is started. When the IID beeps—indicating it’s time to give a rolling sample—the driver usually has five minutes or so to blow into the tube. IIDs ask for rolling samples at random intervals that might range from five minutes to one hour apart.

Testing positive for alcohol on a rolling test typically won’t shut off the car. But the IID will record the positive result, and the court and Department of Motor Vehicles will likely find out about it. Some IIDs will also honk the horn and flash the headlights if they detect alcohol on a rolling sample.

When IIDs are Required

First-offense DUIs. Many states, including Hawaii and Oregon, require all motorists convicted of a DUI—even first offenders—to install IIDs. In a state like New Jersey, on the other hand, the judge can require an IID for a first DUI, but must do so if the driver’s blood alcohol concentration (BAC) was .15% or above. In other states, like Maryland, judges simply have the option of ordering IIDs in first-offender cases. (Haw. Rev. Stat. Ann. § 291E-61 (2016); Or. Rev. Stat. Ann. § 813.602 (2016); N.J. Stat. Ann. § 39:4-50.17 (2016); Md. Code Ann., Transp. § 27-107 (2016).)

Repeat-offense DUIs. Lots of states require IIDs for DUI repeat offenders. For example, in Georgia and Florida, an IID isn’t mandatory for a first DUI, but generally all motorists convicted of a second DUI within a five-year period must have an IID for at least one year. (Ga. Code Ann. § 40-5-63 (2016); Fla. Stat. Ann. § 316.193 (2016).)

Hardship licenses. A driver whose license is suspended because of a DUI can often get a “hardship” license (sometimes called a “restricted” or “Cinderella” license). A hardship license is generally for driving only to and from places like school, work, substance abuse treatment, and medical appointments. In some states, IIDs are mandatory for all drivers with hardships licenses.

Questions for a DUI Lawyer

  • How much will I have to pay to install and maintain an IID?
  • Is there a way to hide an IID so friends and family who ride in my car won’t see it?
  • Do I have to install an IID on every car I own?
  • Can my spouse drive my car while an IID is installed?
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