While the legal limit for driving under the influence is .08% BAC across the country, the BAC limits at which the device will allow you to drive vary from state to state, but are commonly .02% to .04%. So long as the driver’s BAC is below the pre-set limit, the car will start, however, the device requires retesting at set intervals when driving to prevent the driver from simply having someone else start their car initially or having a drink along the way. Alcohol ignition interlocks are required to meet standards set by the National Highway Traffic Safety Administration (NHTSA). These standards ensure that the devices are reliable.