It's been described as a buzzing sensation, a tingling, an oscillation, movement, pure stimulation and, in the case of body-modification expert Shannon Larrett's encounter with a too-powerful antitheft gateway at a retail store, "Like sticking your hand in an ultrasonic cleaner."
Body-mod artists Jesse Jarrell and Steve Haworth's original idea was to implant a magnet to carry metal gadgets. It turns out that doesn't work: If you try to carry something magnetic on your implant regularly, the pinched skin between the magnets dies and your body rejects the implant. But they came up with a new application when a mutual friend suffered an accident that left a shard of iron in his finger. He worked with audio equipment, and found that he could tell which speakers were magnetized from the sensation that passed through his finger at close range.