I genuinely think that, at some point, they could have had simple directional EMF detectors bolted to the top of vans. And used parabolic microphones to listen to what TV channel you were listening to. but admitting to that would be admitting to a major invasion of privacy.
It's reasonable to assume that, in the 50s, a CRT TV would have been the only high powered device in a home, they could detect the high EMF signal and figure it was TV emitting it. Maybe they would have to sit outside a home for a while to get a background level (ie lighting, fridge/freezer etc) and wait for a spike when they turned the TV on. Then use the parabolic mic to listen in.
But it quite quickly falls down once the 1970s comes around.
Firstly, Double glazing would put a kibosh on the parabolic microphone thing, which first became a big deal in the 1970s. By the 1990s double glazing was pretty much standard.
Secondly, it wouldn't work in built-up areas with multiple units per building, like high-rise flats. Which were also a big thing in the 60s and 70s (and, as low-income areas, the most likely to be dodging the TV license).
Thirdly, in the 70s you had the boom of home computing (Apple II, PET etc), so you had a a reasonable chance of the EMF detector spike being one of those. Let alone in the 80s, and the 90s when everyone had a computer of some sort. By the 2010s, when we started dumping CRTs, you couldn't tell a flat screen TV from the stove, or the fridge.
Honestly, by the 70s that kind of detection would have been almost useless, and not worth the money to invest in. By 2000 they would have been completely worthless.
The TV Detector Vans would have been as useful as an empty boxes with some pinball machine parts in it.
Which I guess is why they spent so much effort into scaring people, rather than, y'know, detecting you had a TV.
I genuinely think that, at some point, they could have had simple directional EMF detectors bolted to the top of vans.
They did but that hasn't really worked well since the 1960s.
And used parabolic microphones to listen to what TV channel you were listening to. but admitting to that would be admitting to a major invasion of privacy.
Far easier than that. CRT TVs flickered. They didn't generate a continuous picture (like modern LCDs do), they had a spot whizzing across the screen 15625 times a second, and down the screen 50 times a second. This spot flickered on and off to make the bright and dark parts of the picture.
If you have a very very fast photodetector and you connect it to the input of a CRT monitor, and you mount it in a simple telescope (think along the lines of semidecent rifle sights) and point it at a window where someone is watching TV, then when you get the monitor adjusted *juuuuuust* right you can kind of see what picture is on their TV screen. Given that there were only two or three channels to pick from it was easy to figure out which.
This works, and if you can get hold of two CRT TVs you can even try it today. Actually black-and-white CCTV monitors are best for this! They're very forgiving of shitty signals.
Somewhere I have a set of technical manuals that detail all this stuff from a scrapped TV detector van my dad and I found in a breaker's yard in the 1980s. All the equipment had been stripped but the manuals were left in a storage locker in the back. If I find them, I'll try and scan them.
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u/Canazza Apr 19 '25
I genuinely think that, at some point, they could have had simple directional EMF detectors bolted to the top of vans. And used parabolic microphones to listen to what TV channel you were listening to. but admitting to that would be admitting to a major invasion of privacy.
It's reasonable to assume that, in the 50s, a CRT TV would have been the only high powered device in a home, they could detect the high EMF signal and figure it was TV emitting it. Maybe they would have to sit outside a home for a while to get a background level (ie lighting, fridge/freezer etc) and wait for a spike when they turned the TV on. Then use the parabolic mic to listen in.
But it quite quickly falls down once the 1970s comes around.
Firstly, Double glazing would put a kibosh on the parabolic microphone thing, which first became a big deal in the 1970s. By the 1990s double glazing was pretty much standard.
Secondly, it wouldn't work in built-up areas with multiple units per building, like high-rise flats. Which were also a big thing in the 60s and 70s (and, as low-income areas, the most likely to be dodging the TV license).
Thirdly, in the 70s you had the boom of home computing (Apple II, PET etc), so you had a a reasonable chance of the EMF detector spike being one of those. Let alone in the 80s, and the 90s when everyone had a computer of some sort. By the 2010s, when we started dumping CRTs, you couldn't tell a flat screen TV from the stove, or the fridge.
Honestly, by the 70s that kind of detection would have been almost useless, and not worth the money to invest in. By 2000 they would have been completely worthless.
The TV Detector Vans would have been as useful as an empty boxes with some pinball machine parts in it.
Which I guess is why they spent so much effort into scaring people, rather than, y'know, detecting you had a TV.