I get the best reactions from a simple, cheap, Haunted Key from Fun Incorporated. I hand it to people, and tell them to hold it, twist it, press it, pull it, etc, and be sure that there are no strings, buttons, springs, or such. Then I have them press it to the side of something metal-a fridge, file cabinet, or such-and let it go. When it falls, I point out that it is not magnetic. Then, I ask them to pick it up, and place it in my open palm. I then proceed, or make needed adjustments to the placement before I proceed. Then, I tell the people to watch my hand closely, as I concentrate on the key in my left hand, and gesture 'magically' with my right hand.
I show strain on my face, and let my eyes bulge a bit.. They see no tipping, or tilting, or such of my hand...but the key rolls over. It spooks people. I can repeat endlessly, if I choose to, and no one catches on. An imperceptively minute rolling of my elbow, or a miniscule lifting of my thumb, goes un-noticed. The Haunted Key sells for between $3.95 and $10.95, depending upon where you get it, and when. It takes some experimentation to get the best placement for your hand, as the muscles, and tendons-of the palm, and fingers, which differ somewhat from hand to hand-play a more important part in the effect than does gravity, or such...at least such is so in the way that I do it. I have used the Haunted Key on: drunken partiers, sober police officers, mystically inclined women, imaginative children, and others, and it never fails to mystify...because my palm remains so level, and motionless. The trick is cheap, it is always ready, it is instantly useable with no real set up-apart from the placing of it in your hand-it works well (if you practice sufficiently), it obviously is not gimmicked in any of the classical manners (wires, magnets, etc), and non-magicians can't figure out how it is done. Some who see it become afraid. Others become worhipful fans of their new mystical guru. Others become determined to figure it out...but fail.