A borrowed ring is locked on a 4 digit combination brass lock and, the dials are mixed.
Spectator can test that the lock cannot be opened.
Spectator thinks of a 4 digit number & dials them on the lock.
This proves to be the secret numbers that opens the lock!
Mechanical, nothing to break Nothing added or taken away No electronics parts, no remote control No magnets, no PK rings No threads, no wires No buttons, no switches No gravity switch, no directional limit No timers