How The Ignition Interlock Device Works

Ignition interlock devices are one the newest ways to cut down on the number of people who drink and then drive.

But how do ignition interlock systems work?

First, the device is installed in the vehicle (typically in the glove compartment on the passenger’s side). It is then hard wired to the engine’s ignition system.

When you are ready to drive the vehicle, you will have to blow approximately 1.5 liters of air into a handheld alcohol sensor unit. This unit is normally located on the vehicle’s dashboard. If your breath alcohol content is over a preset limit, the device will not allow the car to start. These preset limits from state to state, but typically are in the range of .02% to .04%.

Some ignition interlock devices are also designed to give “rolling tests.” These are tests that take place once driving has begun. The tests occur at random intervals, from about 5 minutes to 30 minutes after the car has started. These tests are designed to keep the driver from having a sober friend blow into the ignition interlock device. It also prevents the driver from drinking alcoholic beverages once the car has been started.

If the driver fails to provide a breath sample or had a BAC level over the preset amount during one of these rolling tests, the ignition interlock device will issue a warning and an alarm will go off. These alarms can consist of the horn honking or lights being flashed on and off until the ignition is turned off. However, the ignition will not automatically shut down while the car is being driven.

The ignition interlock devices contain a computer chip that records your BAC content when you take the breath tests. If your BAC is over a certain limit, either when trying to start the car or during one of the rolling tests, this report can be downloaded and provided to law enforcement or the court. The reports will also note if the device has been tampered with.

Monthly maintenance is performed on the ignition interlock device. This consists of downloading the data logs from the tests and checking to see if the device was tampered with. All pass/fail results must be maintained. The data logs will also show whether the driver failed to submit to a random or rolling test.