So, looking up Faraday cages, because I had no clue, I came across a shoplifting sight. If my dogs go missing, and you all start sleuthing me, let me save you the trouble - "The Art of Shoplifting" will show up. Wow, what a bunch of leeches on society these people are - one person has been shoplifting for 11 years! Karma's gonna be a beeotch.
Anyway, so, one of the things I found out is that a "Faraday" container can be several layers of tin foil (to hide security tags). But, am I dense, or won't the metal detector pick up the tin foil?
Electricians and shoplifters would likely know about Faraday boxes/cages.
My treasure hunting metal detector hits on foil. I can discriminate it out but some foils have the same readings as some rings so I leave it in. Having no idea what settings the FBI was using on the detectors they were swining in the Irwin yard, I have no idea if they would hit on foil or not. I should dig out my detector and swing it over an old phone to see what it reads.