One way to cheat at Chess is to get information from the outside from computers. A particularly fool proof way of hiding something is in the good old prison pocket. When Hans Niemann was accused of cheating, a lot of people wondered if he had used this particular method. Several prototypes were then made and used to prove the concept.
Those confused, it would work with some kind of vibration code. It doesn't need to be elaborate - just a code to look at a certain square. If he takes longer than 15 seconds or something, someone would be looking at a computer to calculate the best move, then vibrate the code of the square that it would move to. That's all they would need to figure out what to do.
It doesn't even need to be that complex. Sure-fire confirmation that there is a pivotal move can help a top level player slow down, analyze, and make a better play than they would normally. All you really need is a single signal to tell them they have access to a brilliant move, and that alone can turn around a game.
Don't you watch chess matches? Meaning we would see someone pulling something out of his ass and then trying to make sense of what scribbles were still legible through all the shit smears