What keeps the magnets from falling out? Are they connected to bone?
This is called a transdermal implant. It basically has a broader bottom than it has on the sides, kind of like a cufflink. The skin heals around it over time, and it becomes a part of you eventually (assuming its not rejected by your body)
He probably does lots of explaining on TSA scanners at airports.
If he goes through THz scanners and holds his hands parallel to the sides of the scanner they probably wouldn't show up at all.