Try an experiment. Put your cell phone in a microwave and close the door. DO NOT ACTIVATE THE MICROWAVE OVEN!!!

Using another phone, dial your cell phone.

99% of the time, you will hear it ring from inside the oven.

A steel file cabinet is a better Faraday cage. Just put cardboard boxes inside and put your electronics in the cardboard boxes. This keeps them from getting too close to the metal sides.