Status of State Ignition Interlock Laws
Mothers Against Drunk Driving (MADD) maintains a website listing the status of state laws regarding alcohol ignition interlocks. An alcohol ignition interlock is a small device which is installed into the starting circuit of a vehicle. A driver must blow into the device; the vehicle will not start if the driver has measurable alcohol (set to a predetermined level) in their system. If the driver does not have alcohol above the measurable level, the vehicle will start. Interlocks may be set for "running retests," which require a driver to provide breath tests at regular intervals, preventing drivers from asking a sober friend to start the car.
http://www.madd.org/drunk-driving/ignition-interlocks/status-of-state-ignition.html and related web pages.