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