In 1923, inventor imagined that people of the future might carry a flashlight-sized push-button radio beacon, making street crime a thing of the past. Inventor Aubra R. Dunham even included illustrations for how to make your own “radio gun” These “guns” weren’t offensive weapons, but rather hollowed out flashlights that could act as a radio transmitter, alerting nearby listeners (and perhaps one day the police directly) that help was needed. Less than 10-percent of American households had a radio receiver in 1923.”]
Source: https://gizmodo.com/google-glass-is-no-more-the-future-of-safety-than-radio-1278179559