An IID is an ignition interlock device, which is essentially a “breathalyzer” for your car. It is installed in your vehicle by a certified installer and requires you to blow into the device each time you start your car. If alcohol is detected, the car will not start. Drivers also often have to blow into the device at random intervals while driving. The device needs to be calibrated regularly to ensure it is functioning as designed and to make sure it has not been tampered with.