History of obsolete car audio, part 1: Early radio | Hagerty Media
The human need for music is inarguably strong. These days, if you're cruising in your Tesla and you want to hear My Green Tambourine, you just say, "Play My Green Tambourine," and your stereo does exactly that. So it's difficult to imagine the lengths to which early enthusiasts went so that we could all hear music in our cars. https://www.hagerty.com/media/automotive-history/history-of-early-radio/
Until the Transitone, all car radios had to be run with the engine off. So, if you parked and turned the car off, you could listen, but not while driving. The Transitone was the first that could be listened to while driving.