I have recently spent more time on EMP research and testing and have come to several conclusions. The way I am now testing my Faraday cages is by placing a cell phone inside and seeing if it will ring. This has lead to some interesting results. The first thing I found was that the use of a microwave oven for a Faraday cage is very questionable. They will not block a cell phone transmission.
A 50 cal military ammo can lined with styrofoam with the rubber seal still intact was successful in blocking cell transmissions. I have always been told to remove the seal or it won’t work. Another thing that I tried was a tin can with a friction type lid lined with a non-conductive material, similar to the cans you buy popped popcorn in. These worked well. You may want to sand the inside of the lip of the lid to make sure you get good contact.
The last thing that I tried was the Faraday Bag distributed by TechProtect. This is a Milspec bag and seems to work well. It blocks cell phone transmission. I talked with the owner and saw a video of one of the tests he ran on the bags. He placed a cell phone inside a bag and placed it in a microwave oven. He then turned the oven on. It made a nice light show. When removed from the bag the phone still worked. He then placed the same phone in the microwave without the bag and turned the oven on. This killed the phone.
Based on these results of these tests and the advice I received from TechProtect. I am double bagging everything. The TechProtect bags while looking similar to a normal Mylar bag have some definite differences. They are thicker and have an anti static coating on the inside. In addition, they are ziplock. This lets you take out and use your electronic toys and put them back without damaging the bags. The bags come in various sizes. They run from sizes small enough to house your cell phone to big enough to protect the tower to your computer. The prices are affordable, when you consider the value of your electronics.
For my own electronics, I am placing the most critical in one of the Faraday bags and then inside a second container. The choice of the second container will depend on size. Sometimes this will be two of the bags.
I now feel comfortable that I have a system that I can have faith in that my electronics will survive. The bags are available on the internet or you can purchase them through DisasterStuff, their link is on the right side of this page.