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I've heard from more than a few Brits that if you own a TV but don't pay your license fee, they'll come after you with unexpected visits and or fines.

Here is an example article debating their existence.

Even if you smuggle your TV into the country and set it up in a windowless room, supposedly they still have the technology to find out.

Do the BBC have TV detector vans and what technology do they use to find people who have are not paying a license fee?

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  • New Scientist claim some are fake and some are real, but I can't read their references to check why they say that.
    – Oddthinking ♦
    Commented Aug 8, 2011 at 2:01
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    It was possible to detect the leaking signal from a CRT tube from a distance through the leakage of signal from high voltage electronics used to fire the beam at the screen.
    – Stuart Woodward
    Commented Mar 4, 2012 at 22:42
  • see en.wikipedia.org/wiki/…
    – GEdgar
    Commented Sep 5, 2016 at 13:42
  • I believe old CRT systems threw out enough electromagnetic radiation to be detectable, but nowadays that technology is all but dead. I suspect they just data-mine their licensee database against a database of all residences in the UK and assume that any residence not on the TV license list has an unlicensed TV. The detector vans (if they exist, I've never seen one!) probably exist more to scare people than to actually detect TV equipment.
    – GordonM
    Commented Sep 5, 2016 at 14:53
  • physics.stackexchange.com/a/277954/47511
    – Count Iblis
    Commented Sep 5, 2016 at 20:57

2 Answers 2

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For a TV to be able to interpret the information, the high-frequency input is mixed with a local oscillator signal. This is the signal that the detector van can pick up.

enter image description here

Heaps more info here

We have a very similar system in Sweden. The IT magazine Ny Teknik wrote an article called "Yes, you can detect flat screen TV's as well", to debunk the somewhat popular claim to the contrary. Article (swedish), Terrible Google translate.

The article makes the following points (my translation):

New LCD TV's can be detected as long as they have a mid-frequency receiver that modulates the broadcasted TV signal to a base band signal. Its components are subsequently demodulated to become image- and sound signals, respecitvely.

...

TV detection is entirely independent of what technique is used to display the image to the viewer. LCD or plasma makes no difference. VCRs, TV-cards for computers and video cameras with built in TV-tuner has this oscillator as well.

The shift to flat screens does not as such present any problem to the TV detectors. What's worse is the shift to digital TV. If you have a TV receiver that only receives digital signal then there is no local oscillator for the detectors to detect.

The problem with TV detector vans is not that they don't work at all, but rather that they are just now ceasing to be effective, as we're moving towards exclusively digital signals. As TV detection yields diminishing returns, the cost/benefit balance will soon turn TV detection into an unreasonable endeavour.

Techniques that are not as likely to go out of date include:

  • Requirement for TV retailers to report all purchases
  • Phone calls and house visits to try and hear/see a TV

Eye witness won't legally get them very far, though, and you are never required to let such visitors inside your house. Still, this is usually enough to manage to coerce most people caught escaping their license into paying up.

I'm not familiar with the particulars of BBC, but I doubt kidnapping was ever a part of their profession.

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  • 2
    The link you cite looks more like one of the sites we'd like to debunk here than a reputable, trustworthy source.
    – Lagerbaer
    Commented May 18, 2011 at 15:22
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    Are you suggesting that, in Sweden, the government (?) will ring you up to try to tell if there is TV sounds in the background? I'd like to see a reference for that; sounds a little too Big-Brother-ish for me.
    – Oddthinking ♦
    Commented Aug 8, 2011 at 1:47
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    "If you have a TV receiver that only receives digital signal then there is no local oscillator for the detectors to detect." Digital TV receivers still have local oscillators. It's a basic RF receiver requirement, and digital signals are still RF signals.
    – Adam Davis
    Commented Aug 8, 2011 at 5:33
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    @Odd: It's not actually the government. The public service licensing body is a private corporation. See the link How is the radio and TV fee inspection done? in their FAQ for a reference to the fact that they'll call you; as for the listening part, well, I can only anecdotally confirm that they're assuming that everyone has a TV, and lets that set the tone of the conversation; if they hear the TV being on, they'll certainly push that fact.
    – David Hedlund
    Commented Aug 8, 2011 at 6:49
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    Aside: I am smiling at the idea that the normal movie trope excuse when you are being contacted by authorities: "Hey! What is the screaming in the background?" "Oh, it's just the TV." becomes, in Sweden: "Hej! Is that a TV in the background?" "Oh no! It's just a person screaming for their life."
    – Oddthinking ♦
    Commented Aug 8, 2011 at 8:17
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No.

The BBC and enforcement agency have not provided any technical details on how these devices are supposed to work: https://en.wikipedia.org/wiki/Television_licensing_in_the_United_Kingdom#TV_detector_vans

There is some spculation here: http://www.bushywood.com/tv_detector_vans.htm

If the detection equipment works in the manner described above then it is next to useless, because the rules state that you do not need a licence to watch material that is not being broadcast in real-time: http://www.tvlicensing.co.uk/faqs/FAQ15

Televisions don't usually disable this oscillator when not displaying broadcast signals. Many types of set top box also have these oscillators in them too. So the TV detector van would get a positive signal for an oscillator, but not be able to tell if the user was actually watching broadcast TV and thus in need of a licence.

There is also the issue of buildings with multiple TVs, especially student residences but also blocks of flats. It is unlikely that equipment in a van could detect when someone in such a building is watching TV illegally. How would it even determine who the viewer is? The type of antenna seen on TV detector van photos (see above links) looks similar to a TV aerial, a type that is purposefully not too directional and thus unlikely to be able to pick out individual TV sets. They do not appear to be motorized or capable of being aimed in any case.

The TVLA has switched its advertising to emphasising the use of its database in recent years. This is the primary method by which they "detect" people who don't have a licence. The assumption is generally that everyone needs a licence, unless you tell them otherwise (see the FAQ answer above, they view it as your responsibility to call off their harassment and you need to do it every couple of years).

Edit: As Geoff points out, this technology would be completely useless for detecting streaming of live TV, which also requires a license.

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    From a conversation with someone who worked for the TVLA, this is exactly what they do. Why go to the expense of technology that is now obsolete with the advent of on-demand TV over the internet when you can just look to see who's not paying. One of the reasons why the whole licence model is up for revision.
    – GeoffAtkins
    Commented Sep 25, 2015 at 13:41
  • With streaming, the BBC can shape packet sizes to a recognisable pattern, and that can be detected. Even if you go through a VPN.
    – gnasher729
    Commented Sep 8, 2016 at 10:04
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    Even if they did manage to shape packets in a controllable manner, how would they detect them on your LAN or passing through your broadband connection? Also, some VPN providers use interface crowding to prevent such pattern recognition.
    – user18902
    Commented Jan 3, 2017 at 9:22
  • In Norway (which also got license for TV) it's not what you watch which is the question, but whether or not you could watch - the fee is for the TV. If you got a tuner - TV with tuner, VCR with tuner, DVD-recorder with tuner, Sat-box with tuner - then you must pay. (There is also a tax on parts - ie. the tuner-component.) The exception is if the tuner is physically removed (from the TV etc.) or usage of it is blocked. The latter can be done by a authorized TV-repairman, who solders on metal-caps on the antenna- and satellite-connectors, and then sends a work-report to the authorities.
    – Baard Kopperud
    Commented Jan 20, 2017 at 18:10

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