An Ignition Interlock Device, referred to as an "IID," is an after-market device which is installed in a vehicle. The IID is connected to the starter or ignition, or other onboard computer system of a vehicle. The device prevents a driver from operating the vehicle if the driver has been drinking. Before starting the vehicle, a driver must blow into the device; if the driver's BAC is at or over a pre-set limit (0.02 in Vermont) the IID will not allow the vehicle to start.
Detailed explanations of DMV Administrative Rules