An ignition interlock device in a Pennsylvania DUI case is a device that would be installed in the driver's car to not allow the driver to drive the car if they have been drinking. The driver would have to blow into the ignition interlock device, it's similar to a breathalyzer in that sense, and the ignition interlock device would determine if the person had been drinking. If the person had been drinking the car would not start.
This device would be required in certain instances as part of a DUI sentence if somebody were to be convicted or plead guilty to a DUI. It could be a required part of a sentence and it also could be or would be required to potentially get your driver's license restored if your driver's license is suspended as part of a DUI sentence.
Having an experienced Pennsylvania DUI attorney will help you best understand what your rights are with a DUI case and they'll help you best defend against a DUI case. They should be involved as early as possible in the process.