Radio without electricity, the so-called intercom, had already been invented before the war, probably in 1929. I remember radio engineering magazines from the communist period showing diagrams on how to construct such a device. Once, using a transistor, a loudspeaker from an old telephone, a variable capacitance capacitor from an old radio and an antenna in the form of a wire, I also managed to build something like this. The energy to power the speaker comes directly from the transmitter, but there is very little of it, but enough for very quiet listening to the radio.
