I thought I would see if these faraday bags can really block RF signals, so I used my NetAlly Aircheck to monitor my cell phone's wifi while I pinged it from another computer. I figured I have the tool and a client asked me if those bags actually work, so I figured why not give it a try.
I find that a lot of portable wifi devices cycle the wifi off if there isn’t any traffic, hence the ping from the other computer.
I was pleasantly surprised that the bag did block the wifi signal from my phone. I repeated the test several times to be sure and even noticed that the wifi icon on my phone actually disappeared.
The only criticism I would have about the bag is that it should have had a loop or carbineer.