Radio

Although its technology existed before the turn of the century, the radio didn't take off as a communications medium until the 1920s, giving rise to live news and entertainment programs. The radio would prove to be a galvanizing force during World War II, and it continues today to play a vital role in disseminating information. New portable, battery-less radios that operate by cranking a small handle on the side to generate electricity allow anyone in the world to listen in, helping make the radio probably the most accessible communications device on the planet.

Source: http://content.time.com/time/photogallery/0,29307,2026224,00.html