How Ignition Interlock Devices Work

How Ignition Interlock Devices WorkIgnition interlock devices operate along a simple principle – the vehicle cannot be started if the driver has a certain preset amount of alcohol in his or her breath, or, more commonly, any amount at all.

Ignition interlock devices are becoming more and more common in California DUI / DWI cases. An experienced California drunk driving attorney can determine whether an ignition interlock device may be required in each individual case.

Ignition interlock devices are installed into a vehicle’s steering column and sealed with tamper-proof tape. The driver is instructed how to use the device using a special breathing technique meant to prevent others from taking the test in order to start the car. It is a criminal offense in California to assist anyone in tampering with an ignition interlock, or to blow into the tube to start the vehicle for another driver.

The devices operate similarly to breath-testing machines used by police during a drunk driving investigation – the driver breathes into a collection tube, and the device measures his or her breath alcohol content (BAC). Some devices are set to tolerate a low BAC that is well below the legal limit for driving. More commonly, the device will not allow the vehicle to start if the driver has ingested any alcohol at all.

Once the driver has provided an alcohol-free breath sample, the vehicle will start, but “rolling re-tests” are required every five to 20 minutes to keep the engine running. The purpose of rolling retests is to ensure that the driver, not another party, provided the alcohol-free breath test that started the car. The device keeps a record of each test, as well as any attempts to tamper with the equipment.

Although ignition interlock devices were once discretionary in multiple-DUI cases, they are now mandatory. Courts also can order the device installed on a first-time drunk driving case. Some judges have been known to order the device installed in any first-time DUI / DWI cases where the driver registered a blood alcohol content (BAC) of .10 percent or greater.

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