Two containers with screwed on caps and a dice is given out to the audience for inspection. They are then ask to place a face of the dice face up in the smaller container and screw tight the cover. This container is then placed into the larger container and the cap is screwed as well. All these are done while the magician’s back is turned away.
There’s no way the magician can see through these secured containers. But by bringing the container near the magician’s ear, he is able to listen to what face of the dice is facing up.
Very amazing and simple magic.