<story><title>TV detector van</title><url>https://en.wikipedia.org/wiki/TV_detector_van</url></story><parent_chain><item><author>dsr_</author><text>The warrant revealed that a BBC contractor had used an &amp;quot;optical detector&amp;quot; to reveal the possible presence of a TV.[10] The warrant stated that: &amp;quot;the optical detector in the detector van uses a large lens to collect that light and focus it on to an especially sensitive device, which converts fluctuating light signals into electrical signals, which can be electronically analysed. If a receiver is being used to watch broadcast programmes then a positive reading is returned.&amp;quot; [10] The BBC stated that this was strong evidence that a set was &amp;quot;receiving a possible broadcast&amp;quot;.&lt;p&gt;According to The Comptroller and Auditor General of the National Audit Office, &amp;quot;where the BBC still suspects that an occupier is watching live television but not paying for a licence, it can send a detection van to check whether this is the case. TVL detection vans can identify viewing on a non‐TV device in the same way that they can detect viewing on a television set. BBC staff were able to demonstrate this to my staff in controlled conditions sufficient for us to be confident that they could detect viewing on a range of non‐TV devices.&amp;quot;&lt;p&gt;---&lt;p&gt;That device description is entirely consistent with a video camera, perhaps with a telescope in front of it, used for peering through people&amp;#x27;s windows.&lt;p&gt;Does this put the BBC at risk of violating anti-peeping-Tom legislation?</text></item></parent_chain><comment><author>jarvist</author><text>No, it sounds like a telescope focusing onto a single pixel (i.e. just the back of the curtains), and then using the output from this pixel with a lock-in amplifier tied to the broadcast signal. The sensitivity would be enormous due to the lock-in.&lt;p&gt;With a CRT you would be able to do this with &amp;lt;microsecond resolution as the scan lines went across.&lt;p&gt;In today&amp;#x27;s LCD world, I guess something similar could be done for a whole pixel-average of a whole frame, and then look at the time-series of that to correct for lag in digital television &amp;#x2F; internet etc..</text></comment>
<story><title>TV detector van</title><url>https://en.wikipedia.org/wiki/TV_detector_van</url></story><parent_chain><item><author>dsr_</author><text>The warrant revealed that a BBC contractor had used an &amp;quot;optical detector&amp;quot; to reveal the possible presence of a TV.[10] The warrant stated that: &amp;quot;the optical detector in the detector van uses a large lens to collect that light and focus it on to an especially sensitive device, which converts fluctuating light signals into electrical signals, which can be electronically analysed. If a receiver is being used to watch broadcast programmes then a positive reading is returned.&amp;quot; [10] The BBC stated that this was strong evidence that a set was &amp;quot;receiving a possible broadcast&amp;quot;.&lt;p&gt;According to The Comptroller and Auditor General of the National Audit Office, &amp;quot;where the BBC still suspects that an occupier is watching live television but not paying for a licence, it can send a detection van to check whether this is the case. TVL detection vans can identify viewing on a non‐TV device in the same way that they can detect viewing on a television set. BBC staff were able to demonstrate this to my staff in controlled conditions sufficient for us to be confident that they could detect viewing on a range of non‐TV devices.&amp;quot;&lt;p&gt;---&lt;p&gt;That device description is entirely consistent with a video camera, perhaps with a telescope in front of it, used for peering through people&amp;#x27;s windows.&lt;p&gt;Does this put the BBC at risk of violating anti-peeping-Tom legislation?</text></item></parent_chain><comment><author>gnode</author><text>It&amp;#x27;s not a video camera in the conventional sense, necessarily.&lt;p&gt;You could also collect unfocused light emissions, such at those reflecting from walls and ceiling, and correlate their luminance and chroma fluctuations over time with those of live TV. This would not intelligibly perceive non TV light signals, and so be less of a privacy concern. Additionally this would work if the TV&amp;#x27;s image is not visible.</text></comment>