What Is an Ignition Interlock Device?

The Ignition Interlock Device (IID) or Breath Alcohol Ignition Interlock Device (BIID) is an ingenious mechanism for curbing drunk driving by making it impossible for the inebriated driver to start their car.

The Ignition Interlock works by first making use of a breathalyzer like device mounted on a car’s dash.  Prior to the car’s ignition being activated, the driver must use the breathalyzer. The results of that breath alcohol test decide whether or not the car can be started.  The specific BAC (blood alcohol concentration) allowed depends on the allowable level in each locale, but is generally between 0.02% and 0.04%.

Most IIDs will require random breath samples at various times while the engine is running. This is a measure put in place to make fraud less likely.  In other words, a drunk driver could have a friend pass the initial breathalyzer test only to get behind the wheel and drive under the influence. This way, the driver is required to randomly provide another breath sample in order to continue driving. Depending on the specific IID or BIID device, a failed test while driving may result in a horn sounding, lights flashing or other similar reactions until the vehicle comes to a stop and the ignition is turned off.

Contrary to what you may have heard, a failed IID test will not result in the power being turned off when the vehicle is already started. To do so could have dangerous, even fatal repercussions and would not help to keep the roads safer.

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