An ignition interlock device (IID) is a breathalyzer-like instrument. It is installed in a vehicle to prevent it from starting if the driver’s BAC is above a pre-set limit. In South Carolina, an IID may be required for individuals convicted of DUI offenses with a BAC of 0.15% or higher. It may also be mandated for those with multiple DUI convictions. The IID requirement's duration depends on the offense's severity and the individual’s prior DUI history.