An ignition interlock device is an instrument installed in a vehicle which requires that the driver blow into it before the car will start. In theory at least, the vehicle will not start if the driver has alcohol in his or her breath. The device may also require that the driver blow into it periodically while driving.
Ignition Interlock devices can be ordered by the court in DUI cases and can be required by the DMV before reinstatement of driving privileges following a DUI suspension. This is typically the case on second or third DUI's. When ordered or required the defendant or licensee has the responsibility to pay for installment and periodic calibration.
IID's are routinely ordered by the court for people convicted of driving on a suspended license when the suspension is DUI related.
If the device is court ordered, the court will often accept proof of sale of the vehicle or transfer of ownership in the vehicle instead of proof of installation of the IID.
Penalties for DUI in Los Angeles and Orange County courts are increasing all the time. We can expect that IID's will be seen as an increasingly likely option for the courts as organizations like Mothers Against Drunk Driving push for them more and more.