What is an Ignition Interlock Device?

South Carolina’s Ignition Interlock Device (IID) Program is managed by the Department of Probation, Pardon, and Parole. The interlock consists of a relay module that is wired into the vehicle ignition system. The device draws a portion of the motorist's breath sample into a fuel cell sensor. The presence of alcohol in the sensor chamber causes the fuel cell to output an increased electrical current which is measured and then translated into an equivalent blood alcohol concentration. If the result of the test is below an alcohol concentration of .02 an encrypted signal is sent to the relay allowing the vehicle engine to start. If the test result is above .02 the vehicle’s ignition system will remain locked. When the device is unlocked the IID is designed not to interfere with the normal operation of a vehicle so while the device can prevent a vehicle from starting, it will not shut down a running vehicle.