The situation was (is) the same in Germany: There is a fee of about 20EUR/month per household in order to fund the public service broadcasting. And in the last century, these "TV detector vans" also have been a thing in Germany.
While the detecting technology can work in theory, it will perform poorly in practice. Think of any dense settling, such as apartment blocks. It will be kind of impossible to determine the exact source of radio signals from the street, at least in the frequency domain and signal strength in question.
They had fee collectors in Germany in the 90s. When I was at university it was common knowledge that you do not have to let them in if they come to your home. A friend's roommate let them in anyways, which cost him 400 DM (that would now be about 500€).
I assume the 500 Euro includes inflation, doesn't it? Oherwise, I have to agree, back the day you didn't have to let these guys in. You didn't, you were save. Just another reason why the switched to a household fee. Regarding that so, not having a TV cable connection at our home, we do watch German public TV through their apps for Fire TV, so not oaying the fee and still wtching would be kind of using "alternative" streaming services, which I did too before Amazon prime and Netflix came about.
While the detecting technology can work in theory, it will perform poorly in practice. Think of any dense settling, such as apartment blocks. It will be kind of impossible to determine the exact source of radio signals from the street, at least in the frequency domain and signal strength in question.