Ignition interlock device

An ignition interlock device or breath alcohol ignition interlock device (IID and BAIID) is a breathalyzer for an individual's vehicle. It requires the driver to blow into a mouthpiece on the device before starting the vehicle. If the resultant breath-alcohol concentration analyzed result is greater than the programmed blood alcohol concentration (which varies between countries), the device prevents the engine from being started. The interlock device is located inside the vehicle, near the driver’s seat, and is directly connected to the engine’s ignition system.

An ignition interlock interrupts the signal from the ignition to the starter until a valid breath sample is provided that meets minimal alcohol guidelines in that state. At that point, the vehicle can be started as normal. At random times after the engine has been started, the IID will require another breath sample. The purpose of this is to prevent someone other than the driver from providing a breath sample. If the breath sample isn't provided, or the sample exceeds the ignition interlock's preset blood alcohol level, the device will log the event, warn the driver, and then start up an alarm (e.g., lights flashing, horn honking) until the ignition is turned off, or a clean breath sample has been provided. A common misconception is that interlock devices will simply turn off the engine if alcohol is detected; this would, however, create an unsafe driving situation and expose interlock manufacturers to considerable liability.

The first performance based interlocks were developed by Borg-Warner Corp. (now BorgWarner, Inc.), in 1969. In 1981, Jeffrey Feit, a student in New Jersey, placed in a statewide innovation contest with a primitive schematic of a breathalyzer based interlock device. in 1983, Hans Doran, a student in Limerick, presented a working prototype at the Young Scientist competition in Dublin. Alcohol-sensing devices became the standard through the 1980s. They employed semiconductor (nonspecific) alcohol sensors. Semiconductor-type (Taguchi) interlocks were sturdy and got the field moving, but did not hold calibration very well, were sensitive to altitude variation and reacted positively to non-alcohol sources. Commercialization and more widespread adoption of the device was delayed pending improvement of systems for preventing circumvention. By the early 1990s, the industry began to produce “second generation” interlocks with reliable and accurate fuel cell sensors.

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