# I saw the Cat Detector van!

**URL:** <https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917>\
**Category:** Miscellaneous and Personal Stuff I Must Share\
**Created:** [October 13, 2018, 11:23pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917 "2018-10-13T23:23:09Z")\
**Posts on this page:** 2\
**Page:** 3

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**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\
**Post date:** [October 15, 2018, 9:50pm UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/41 "2018-10-15T21:50:39Z")

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Claim jumpers? Why those doggone double-crossin lily-livered varmints! I’ll blast the fur clean off their flea-bitten hides!  
Oh, “clam”. Never mind.

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**Author:** ![voltaire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voltaire/32/313_2.png) [@voltaire](https://boards.straightdope.com/u/voltaire)\
**Post date:** [October 16, 2018, 12:01am UTC](https://boards.straightdope.com/t/i-saw-the-cat-detector-van/822917/42 "2018-10-16T00:01:10Z")

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> [@Chronos](#):
>
> They might be looking for the _specific_ variable glow associated with whatever the BBC channels were showing at that moment. It wouldn’t take much processing at all to turn the broadcast signal into brightness as a function of time, and to then compare that to the brightness as a function of time coming from a window.

Yeah, that’s what I meant by variable glow. The variance being the tell-tale part.

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