Nintendo Light Telephone (1971)
Okay so this is pretty interesting. Using solar power (yes really) this weird gadget was able to transport sound. And while Nintendo didn’t invent this technology, it’s application to these weird light-walkie-talkies is pretty amazing.
The sound picked up by the microphone of the Light Telephone is coded into the transmitted light, decoded again by the receiving party’s Light Telephone using a solar cell, and played over the headphone. This creates, in effect, a two-way walkie talkie without the use of radio waves.