The tangent to this is done with invisible ink. https://www.customplayingcardss.com/product-category/poker-cheating-device/poker-analyzer/ https://www.custompla

The tangent to this is done with invisible ink. https://www.customplayingcardss.com/product-category/poker-cheating-device/poker-analyzer/ https://www.customplayingcardss.com/product-category/poker-c... There is a corresponding custom phone that has a hidden camera on the side (facing the deck) that then communicates with some haptic feedback that the cheater is wearing.