A device which disables vehicle use when the operator fails a test, which failure indicates the operator has consumed more than a certain amount of ethanol. More formally referenced in the US by the acronym "BAIID" (="Blood Alcohol Ignition Interlock Device"). The test is currently usually a breath sample analyzed by a fuel-cell.
"I blew my booze nanny, and she falsed on me, so I'm running down the road with my horn honking and my lights flashing. Hope nobody takes it personal and shoots me."