Where's a good place to get magnetic rings for this purpose? I searched Amazon and found things like magnetic bracelets marketed as alternative medicine to cure you. None of the reviews I found mentioned using them as an electromagnetic sensor, so I can't tell if they're useful for the purpose.
There should be a difference in sensation because of the difference in mass of the ring versus implant. An implant, simply because it is so much smaller, should have a stronger reaction, should move or vibrate more, for a given strength of field.
It looked more than a little flashy, and it provided less sensation than it would've implanted, but it worked surprisingly well.