You say simply, but I think that's much more difficult than just detecting the presence of em noise conforming to a broadcast standard.
Anyone that's put an AM radio next to a CRT TV knows it emits em noise.
The CRT itself is, to over simplify, a high voltage capacitor. It's one of the most popular devices used to power hobbyist Tesla coils...
I don't know why everyone seems to think that just because TVs were "receive-only" devices, that they wouldn't emit any sort of easily detectable signal.
Also, when this enforcement began, broadcast was the only source of TV content, so the presence of a TV was generally proof of watching broadcasts. There wasn't really any need to prove the TV was tuned to any particular content.
Now, whether it is a practical, effective method of enforcement that was actually used is another matter.
Maybe poor phrasing on my part, but that's the prevalent theory I've seen for how they do it today. Various other methods of EM leakage might have worked in the past (unproven as far as I know), but modern televisions are so much better built that visible light leakage is believed to be the only effective detection method.
Here's my TV detection method: look at their windows and see if there's a light flickering pattern that looks like a TV (if behind curtains) or maybe you can see the TV
Anyone that's put an AM radio next to a CRT TV knows it emits em noise.
The CRT itself is, to over simplify, a high voltage capacitor. It's one of the most popular devices used to power hobbyist Tesla coils...
I don't know why everyone seems to think that just because TVs were "receive-only" devices, that they wouldn't emit any sort of easily detectable signal.
Also, when this enforcement began, broadcast was the only source of TV content, so the presence of a TV was generally proof of watching broadcasts. There wasn't really any need to prove the TV was tuned to any particular content.
Now, whether it is a practical, effective method of enforcement that was actually used is another matter.