All electronic devices emit electromagnetic energy, which may interfere with the normal operation of electronic devices. In the past this interference was most often noticed as distortion appearing within certain frequencies of a radio. Today, almost every vehicle has some type of electronic system. CAPA requires Electromagnetic Compatibility (EMC) testing on parts that contain active electronic devices, such as HID or LED components, and parts with motors. EMC testing for electromagnetic emissions and immunity ensures that the systems in a vehicle are functioning properly together, and that the systems in surrounding vehicles are not causing interference.