A microwave does have some effectiveness as a Faraday cage, but it's not complete. I worked for a couple companies doing mobile games, and one of the certificat

A microwave does have some effectiveness as a Faraday cage, but it's not complete. I worked for a couple companies doing mobile games, and one of the certification tests during the 3G era was to make sure the app performed gracefully when the signal was lost. Putting the phone in a microwave was the first thing we thought of, but it didn't work well to cut the signal. We tried a couple different microwave ovens. Sometimes it worked if we put the phone in a ziplock bag and immersed it in salt water, then put it in the microwave.