Faraday Cage to block WiFi

[Gyro]

yep, those microwave ovens are double faraday cages with only weak spot from the door, because of the viewing area, still shielded with some holes in the shielding material.glass absorbs also some of the remaining GHz, not all.

Nope, sorry, you haven't got the hang of that one at all. The viewing area is no problem, the window area is covered by a metal mesh that blocks all microwave energy. Just go and look at your microwave oven door and note that its periphery is effectively insulated by plastic mouldings and latch, apart from the two metal hinges, not an RF bond in sight.

As I mentioned previously, the secret of a microwave oven door is the inclusion of a quarter-wave trap right around the periphery, that presents an RF short to the microwave energy trying to escape. It is tuned to form a notch filter that effectively shorts the energy at the Magnetron frequency and RF grounding the door at that specific frequency - it's really a very clever technology to be able to accurately achieve this in a mass produced consumer product.

Here's the relevant patent...  https://patents.google.com/patent/US4523069

you're right in theory, but have you seen/tested in a lab the amount of radiation escaped from the front door? it's not 0, even with the correct sized holes.
where did the oven leaks more? the door obviously
some people talk theory, some consider the real life. i had the same arguments with my boss in france, he always told me the theory then he returnet from emi testing to redo the job
 unfortunately, we must consider real life, otherwise we won't pass approval tests with some theory on paper.
don't take this personally, it's just as it is

Ha, yes that's an easy one, the door... but much more specifically the edges of the door, where the microwave traps are located, rather than the window. The traps have a very high energy attenuation at the 2.45GHz magnetron centre frequency but are not perfect. If you check out the service manual for any commercial microwave oven, you will find that the required leakage tests and energy measurements are carried out using a probe around the edges of the door. There is nothing more real life that a Microwave oven in actual operation, it is theory in action.

I don't want to make a big issue of this anyway. My point was that a microwave oven isn't a Faraday cage. It is a cavity with a door which is not physically sealed (in fact has a very specific gap) and is only protected by a narrow band steep notch filter at a specific frequency, but effectively open to RF at all other frequencies.

As you say, it's just as it is.