Tie a knot in the cord on the badge holder with about 1 inch of cord showing so that it does not fully retract.
Use glue to attach a strong magnet to the cord on the badge holder. Attach the magnet 2 to 3 inches from the knot.
Cover the magnet in felt using more glue for a nicer look and feel. Felt will keep the magnet quiet when performing the trick. The covering will also keep the magnet from feeling cold against your skin.
Secure a loop of fishing line to the magnet using glue. The fishing line should be long enough so that it reaches from the back of your palm to the end of your middle or index finger.
Snap the badge holder to your belt or top of your pants and loop the fishing line around your fingertip, beneath the fingernail. (This trick works best if you are wearing a shirt with long sleeves.)
Put a bottle cap or steel coin on the table, then wave the magnet over the cap or coin.
Release the fishing line from your fingertip, and the magnet and coin will slide into your shirt sleeve.