an ordinary compass is a really cheap EMF detector...when spirits are near,
the needle does not stay on North, and can go back and forth between directions...
and when the needle actually spins, there's a vortex nearby....
i keep a compass on a stand in my bedroom, always pointing due North...
when i'm using my pendulum or the Konxari cards, I have noticed the needle wavers
to the West or East a bit...
have yet to see whether you can ask spirits to waver it on command like a K2 meter's lights...
something to try though