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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 "recei…
You're thinking too much like an engineer 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
Looking for light would also only work until people found out about it, and violators covered their windows.