Campana Mortis means "bell of the dead" in Latin. This is the classic spirit bell stripped back to its essentials. A block of wood (reclaimed walnut), two brass posts, and a small bell that hangs between them on a chain. Your audience member can assemble it themselves.
At the appropriate time you can make the bell ring, even though you can be yards away and with your hands in full view. The dead are speaking beyond the grave.
Nothing under the table. No strings or threads. No batteries to be inserted anywhere.