North Korea banned 22 million people from contact with the outside world, and letters, telephone calls, travel, radio and television were all restricted. People who own radios must register with the police, and foreign brands of radios will be dismantled by the police on the spot, locking the frequency of North Korea's state-run radio stations, welding them and putting them back in their original places. The police will also visit these families with foreign radios from time to time to check whether the radios have been modified.