How can I find out the number of listeners on the radio (by radio communication)?

Question

Radio communication

How do radio stations know how many people are listening to them? For example, autoradio, how do they know that they are not rolling, and that someone is listening to them at all?

Answer 1

Probably through feedback channels, Internet telephone, public opinion poll, etc. and there are often programs on the radio when listeners call the studio, you can count the number of calls.
PS
Your question does not apply to radio communications, but rather to broadcasting.