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Ignition Interlock Devices

Ignition interlock devices (IIDs) are instruments designed to prevent someone from operating a vehicle when the device finds alcohol on the would-be driver's breath. These devices, often installed on vehicles of those convicted of a DUI, essentially are Breathalyzer machines that control the ability to start the car. Almost all states have drunk driving laws allowing or requiring judges to order ignition interlock devices in cars operated by certain drunk driving offenders.

State laws vary greatly when it comes to ignition interlock devices. Specific state drunk driving laws should be consulted to find out whether an ignition interlock is mandatory, or within the discretion of the judge in any given case.

How an Ignition Interlock Device Works

An ignition interlock device works by measuring the driver's blood alcohol content and disabling the vehicle's ignition if the driver's breath contain alcohol. Most IIDs use a lock-out period to prevent starting the vehicle if the device detects more than a low threshold level of blood alcohol content. The lock-out period typically gets longer with each failed test.

During "rolling retests," most IIDs signal the need to provide a fresh breath test. If, within a certain space of time, the machine does not confirm clean breath, often an alarm will sound or the car's horn will honk to prompt the driver to turn off the vehicle. IIDs are not designed to turn off a moving vehicle in the event of a failed retest. Depending on the system in place, the device may save information relating to the failed retest.

Discretionary Ignition Interlock Device Laws

Often, state laws give judges the discretion to order an ignition interlock device for specific classes of convicted drunk drivers, such as first time offenders. Under the laws of many states, IIDs may be used for a portion of the period in which the offender's license would be suspended.

In these situations, qualifying offenders typically must satisfy other sentencing requirements in order to be able to drive with an IID. These requirements can include jail or time, probation, payment of a fine, completion of an alcohol treatment program, and a period of full license suspension, amongst others.

Mandatory Ignition Interlock Device Laws

A growing number of states make an ignition interlock device mandatory, rather than simply leave it to the judge's discretion, in certain types of drunk driving cases. Some states or specific cases may opt for the SCRAM device instead, which also monitors alcohol consumption in general. Some states have begun requiring first-time offenders to have IID's installed. The most common situations in which these states require an IID (should the offender wish to drive) include:

  • Having multiple drunk driving convictions;
  • Having a minor in the car at the time of the incident; and
  • Having an elevated blood alcohol content level.

Ignition Interlock Device Installation and Costs

States have rules surrounding the installation and inspection of ignition interlock devices. Generally, drivers must have the device installed by a state approved installer and must provide proof of installation to the court. Often, state law also requires periodic inspections of the device by an approved installer.

Generally, the offender must pay any fees associated with an IID. These can include fees for the device itself, an installation fee, monitoring or calibrating fees, and a security deposit and/or device insurance fee. Some (but by no means all) states reduce certain drunk driving fines for those able to demonstrate an inability to pay the costs of an IID.


Almost all states incorporate ignition interlock devices into drunk driving sentences for certain offenders. These devices test a driver's breath before allowing the vehicle to be started, and periodically retest breath during the drive. Depending on the specifics of the drunk driving conviction, in some states an ignition interlock device may be required by state law, or may be within the discretion of the judge to order.

Get Help With Your DUI Case From an Experienced Attorney

While attorneys can be particularly helpful in either deflecting or reducing the seriousness of charges against their clients, they also can help at the sentencing stage. If you believe you are a good candidate for an ignition interlock device following a DUI conviction, consider speaking with a local DUI attorney today.

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