Ignition Interlock Device

An ignition interlock device or breath alcohol ignition interlock device (IID and BAIID) is a mechanism, like a breathalyzer, installed on a motor vehicle's dashboard. Before the vehicle's motor can be started, the driver first must exhale into the device; if the resultant breath-alcohol concentration analyzed result is greater than the programmed blood alcohol concentration—usually 0.02% or 0.04%, the device prevents the engine from being started.

At random times after the engine has been started, the IID will require another breath sample. The purpose of this is to prevent a driver from taking an alcohol bottle inside the car and drinking while driving, after the breath sample is provided. 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.