At least in Europe, if enabled by the driver, the car radio listens for EON signals on FM channels, and switches to the indicated channel from whatever is playing (MP3, CD, another channel). They usually do this to indicate that a traffic announcement is happening on the other frequency.

But since this seems to be an FM radio addition, the law should've forced cars to have FM radio as well...

https://en.wikipedia.org/wiki/Radio_Data_System