[flyax]

There are a lot of possibilities, mainly if the cheater has help from someone outside who has information about the game. It's enough to transmit a signal in critical position that something is there.In past, player refused to take off his shoes. Other one has friends who sit in particular order. From other discussions

* a hair of defined length placed in a bowl or glass of water and vibrations at the resonant frequency of that hair would produce visible ripples around the hair. * distant noise such as car horns honking, bass from a passing vehicle blasting dubstep, construction noise, etc. * laser beam through the window visible only with particular contact lenses * a bone-induction speaker or thumper (vibrating device) embedded in them or replacing a tooth * thumpers that can be put inside the soles of shoes that would not be detectable with a regular metal detector

My impression is that the technology is there. If the incentives are high enough, someone can find the way.