How do radio stations know that you’re listening to them? Is there a signal sent back somehow?

Question

How do radio stations know that you’re listening to them? Is there a signal sent back somehow?

In: 2349

Answer 1

https://slate.com/news-and-politics/2002/12/how-do-super-intelligent-billboards-spy-on-your-car-radio.html

They use sophisticated radio receivers that detect RF leakage from your radio that indicates to the receiver what radio station that you’re listening to.

They also do ratings surveys that allow them to know what radio stations you listen to. They ask.

Edit: the outbound signal is extremely weak and it needs a sensitive receiver calibrated for just this purpose and it has to be at fairly close range to be able to detect the carrier wave