The Blackbelt Barrister has a few good youtube vids on Licence Fee collection
View: https://www.youtube.com/watch?v=6o46BHr19Dw
One think legal experts often overlook regarding "detection" is Barb.
Re: stray signals: I used to work for a QUANGO in their space research division in a technical (software) role but used to chat to the very knowledgeable RF radio transmission people and even hack then pre-falt screens they could think of no way the detector vans could operate ands they rekoned they relied on somebody "it's a fair cop ..."
But these days it also comes down to "trust". How much to you trust for profit private data collection companies. Even if you receive through a TV ariel using Freeview, Barb embed software recording what you watch (irrespective of your Freeview device), when and for how long using a device ID which reports this information back to them for analysis which they sell. Whilst they provide a "yellow button" way to "opt-out" you can't opt-out of the BBC tracking.
Barb do state that they don't record personally identifiable data and that every 6 months they'll rotate your device ID, etc. but they are a "for-profit" company collecting data about what I do against my wishes so my natural paranoia means I don't trust them. OK, they can't track me as I've taken steps on my Freeview box and TV to block access to their servers but most people won't and thus if they've chosen you they are getting to know your viewing details ...
Not every device is "selected by Barb", any device can be but they make random selections eg my TV is not currently selected (that might change tomorrow) but my Freeview box is selected - except I've blocked any reporting back to Barb.
People (including me) often joke about tin foil hats and how "big brother is watching" except in increasing areas of our lives these days big brother really is watching.
Ian