Crystal radio
Crystal radios have come and gone many times in history. They were built in the early days of radio broadcasting by amateurs, and people who could not afford a well-made radio. They became popular again during the Great Depression, when money was scarce. During World War II, American soldiers built "foxhole radios" that used a razor blade and pencil point instead of a crystal. (German and Italian troops had equipment to detect normal superheterodyne radio receivers working, so an alternate choice was a wise one.)