Ignition Interlock Devices

Definition: An ignition interlock device is an alcohol breath screening device located in a vehicle, which prevents the vehicle from starting if a blood alcohol concentration of 0.02 (20mg of alcohol per 100mL of blood) or greater is detected.

Executive Summary: Ignition interlocks are found near the driver’s side of the passenger compartment and are connected to the vehicle’s ignition system, not the engine. The purpose of the device is to prevent a person who has consumed alcohol from starting and driving the vehicle.

More Detail: The driver must blow into the device before the car can be started. If the BAC level is above the preset limit, the vehicle will not start. Research has shown these devices to be a popular, effective and relatively inexpensive mechanism for allowing the hardcore offender to drive legally and sober.

Most of the devices have driver recognition or anti-circumvention features, including a data recorder that documents all vehicle uses as well as any attempt to tamper with the device. They can also include a running re-test feature that requires the driver, after starting the vehicle, to supply at least one other breath sample during the trip.

These systems are not foolproof. These devices can sometimes be circumvented, but technological improvements, such as the running re-test, have greatly reduced this possibility. They also do not keep offenders from operating other vehicles, which are not fitted with interlock devices, such as rental cars.

Research does not recommend the use of ignition interlocks as a substitute for licensing sanctions, but rather as a condition of licensing reinstatement after a period of suspension. Early installation is suggested, as opposed to long periods of license suspension which can teach the driver they don’t need a license to drive.


Suggested Audience: Prosecutors, Judges


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