Someone left their cell phone here, it was ringing like crazy. I stuck it in a metal pot with a metal lid to shut it up, it still rang. I later put it in a safe, it still rang, but so muffled as to not be annoying. (Admittedly the safe has a gasket on the door--it provides fire, flood and walking out with the guests protection, it wouldn't defeat a serious burglar.)
How is the signal reaching the phone???