Now turning to external interference, electricity travels through space as electro-magnetic energy. When a licensed broadcaster, such as a radio station, is transmitting and a user’s radio is able to pick up good reception, it is considered desirable energy. If their neighbor is operating a high-powered drill which emits electro-magnetic energy in his garage, and it interferes with radio reception, it is considered undesirable energy or electro-magnetic interference (EMI). Manufacturers of computers have always had to deal with received electro-magnetic energy by using shielding, noise immune logic or balanced drives. Due to the proliferation of digital logic, home computers, printers, electronic games, MP3 players, mobile cell phones and so on, the Federal Communications Commission (FCC) of the United States regulates electro-magnetic emissions of these digital devices so that they do not interfere with licensed broadcasts, wireless phone service, medical equipment in hospitals and radio communications frequencies used by emergency services. In other countries statutory authorities enforce similar regulations.