How Ignition Interlock Devices (IIDs) Work & When Are They Required

Various states, such as Pennsylvania and New Jersey, have enacted laws that require even first time DUI / DWI offenders to have an ignition interlock device (IID). This device is typically the size of an older, larger cell phone, and is installed in a way that it integrates into the starting system of your vehicle, preventing you from operating the vehicle if the IID senses you have a blood alcohol level that is above the limit set on the device.

How Does an Ignition Interlock Device Work?

In brief, the IID is a mini breathalyzer connected to the ignition switch of your car. The machine measures blood alcohol content (BAC) in a manner similar to the portable breath test devices used by police in the field. The devices will prevent the automobile from starting until the intended driver has passed the BAC breath test – i.e. you must blow into the device before you can start your car, and often times, you may be required to blow into it again at various time intervals when you’ve been driving to ensure that you didn’t have someone blow into it for you.

What is the acceptable BAC level to “pass” the IID?

Most machines will lock the starting device of the automobile if the BAC is higher than .02.

Costs Associated with the Device

The ignition lock device, also referred to as an interlock, must be purchased if you’ve been convicted of a DWI / DUI. The cost to buy the equipment, have it properly installed, as well as the monthly maintenance fees is all the responsibility of the person convicted of DUI / DWI.

Typical installation costs vary from $100 to $200 plus any applicable state and federal taxes. In addition, there are monthly maintenance / usage fees ranging from $60 to $120. If the data contained in the device is downloaded to the court or to an attorney there is usually an additional fee for this service. A list of certified IID providers can be obtained by contacting the National Highway Traffic Safety Administration (NHTSA) and can be found online for Pennsylvania and New Jersey.

Conditions that require Interlock

In Pennsylvania, all second and subsequent DUI offenders must have the interlock installed. In New Jersey, all persons convicted for a second and subsequent DWI or for a refusal must get the interlock installed. For a first-time DWI in New Jersey, the interlock is only required if the BAC was a .15% or higher. Otherwise, the installation of the device is not mandatory but is in the judge’s discretion.

How Long Must You Have An IID Installed?

Typically, people are required by law to keep the device on their vehicle for at least one year following their DUI conviction. In addition, the person may have to keep the IID as a condition of reinstating their driver’s license.

The IID Has Tamper Resistant Technology

As expected, many people attempt to get around the use of the interlock. However, the developers of these devices have invented several safeguards to prevent motorists from bypassing the system. For instance, the device will lock the ignition if the person refuses to take the breath test and attempts to start the car. If someone tries to remove the device or disable it in some way, it will lock the ignition. A few manufacturers have introduced rolling retests to deter savvy drivers who get someone to blow for them, then drive off.

The rolling retest works in the following scenario. A convicted DUI offender goes to their vehicle after drinking. They know they will likely fail the breathalyzer test, so they ask a friend to breathe into the machine for them. The friend passes the test and the car starts. However, at some randomly chosen time period, after the car has been running, the machine will require a new breath test. If the DUI offender fails this test the car will shut down and the ignition will lock.

Monitoring By the Device

The interlock system has an on board computer that stores the history of the tests completed by the driver. This historical record can be retrieved either by printing or downloading to a computer. Most device providers have the ability to retrieve the information at 30 day intervals to provide to attorneys and the court.

Does the IID Successfully Deter Drinking and Driving?

Several independent studies have shown that the interlock device has worked well to reduce the number of drunk driving arrests nationwide. Compared to the traditional policy of merely suspending a person’s license, some studies have shown a high percentage reduction in drunk driving. The devices have led to more offenders following the rules of the court and successfully completing their probation period with a reduced amount of recidivism.