Murphy, did you even watch the video??? The microwave did not block the cell phone signal.
The point was that a microwave can't even block a cell phone signal. THEREFORE WILL BE COMPLETELY USELESS for shielding electronics from a much more powerful EMP.
I probably should have gone into a longer discussion on it.. My apologies for not making a complete post.. it can be difficult to explain advanced electrical concepts sometimes and that's compounded by the fact that I'm not a teacher. I have clients that ask me for explanations and I pull my hair out sometimes because every answer I give them just generates a dozen more questions...
Its not that the video is right or wrong, its that it is irrelevant.. Its like saying "I'm going to eat this apple to prove rat poison isn't harmful".. It makes no sense.. It doesn't matter if the cell phone picked up the signal or not, its irrelevant to the question of whether a microwave will protect the cell phone (or any electronics) from an EMP..
Lets elaborate on the experiment a bit for a better understanding...
Take a trashcan and line it with cardboard.. then put a cell phone in a static emp bag and place it in the trash can.. Carry the entire thing to the nearest cell phone tower and try to call the cell phone in the emp bag that's inside the trash can.
It will probably ring.. it probably has at least one "bar" of signal.. Does that mean the home-built Faraday cage won't work? No! It means nothing to the effectiveness of the home built Faraday cage. The reason is that cell phones are highly sensitive devices designed to pick up even minuscule electromagnetic waves. EMP shielding is not about achieving a complete isolation from all electromagnetic energy.. that's nearly impossible.. in fact, based on some physics theories, it is impossible. EMP shielding is about attenuating an electromagnetic wave to a point that it won't damage the item(s) you're trying to protect.
In other words, you can think of it this way.. A Faraday cage is to electromagnetic energy as Sunglasses are to your eyes. You don't need your sunglasses to completely block out all light, you just need them to attenuate that light to a comfortable level. Your Rayban's might do an adequate job on a sunny beach but they probably won't be dark enough if you're trying to Arc Weld..
Now take the trash can back home a few miles from the cell tower and try again.. Does the cell phone ring? Probably not.. Does that mean the trashcan faraday cage is effective against EMP? NO again! Even though the trashcan + emp bag would be an effective Faraday cage, the test is irrelevant in this case because the cell tower is broadcasting a relatively low power signal and your receiver is far away.
There's another angle to consider in all this.. A cell phone is designed to detect and transmit on specific frequencies.. A high altitude nuclear EMP will not just blast out just a narrow band of frequencies, it will saturate most of the electromagnetic spectrum.. and its a big ass spectrum that ranges from long radio waves all the way to the gamma end. The design of your EMP cage must take this broad spectrum into account and not just the narrow band your cell phone picks up.
The good news is that for our purposes, we're just worried about the longer radio waves.. and commonly available electrically conductive materials are quite effective if assembled correctly. The best Faraday cages are multilayered (insulation in between each layer) and each layer should ideally be a different material. Steel, aluminum, copper.. type of thing. This is ideal, but in no way required for our purposes.
Put your device in a good quality static shielding bag and tape it shut.. then put that into another bag.. You now have two layers but they're both made of aluminum.. Now take the bag-in-a-bag and put it in the trash can.. You now have three layers (excellent!) and two different materials (very good!).. That will protect 95% of electronics 95% of the time and that more than enough for us preppers.
Hope that helps,