Blue box
A blue box is a device that someone could use to make free telephone calls. It worked by playing back the same sounds that the telephone company employees used to program their equipment.
The most famous person to use a blue box was John Draper, who went by the name Captain Crunch. Draper taught Steve Wozniak how to build them. Wozniak and Steve Jobs sold blue boxes to fellow students at the University of California, Berkeley. One time, Wozniak used a blue box to call the Pope.
Blue Box Media
Blue box designed and built by Steve Wozniak and sold by Steve Jobs before they founded Apple. Displayed at the Powerhouse Museum, from the collection of the Computer History Museum