Re: Faraday cage with a window ...
That's why, when building a Shielded Enclosure, you use two different bits of kit.
A SELDS (Shielded Enclosure Leak Detection System) to check for RF permeability in the welds and a LISN (Line Impedance Stabilisation Network) to look for signals being radiated down the power lines.
I actually own both of those, though I have no idea why. I should probably find a gullible doomsday prepper to sell them to.