Since even a phone has enough processing power to make Stockfish play better than a super-GM, the Faraday cage isn't enough to prevent, say, someone tapping the position into a computer on their person and feeling for some sort of vibration[1] in response. It takes very little information to represent a position, and commentators have pointed out that the minimum amount of information required to produce a decisive advantage is 1 bit ("A winning move exists").

[1] Yes, the ribald jokes have already been made