I saw the Cat Detector van!

[markn_1]

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.

[voltaire]

@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.