At least for medical implants you get an "implant passport" which lists the implants and their locations, but if it is something that triggers metal detectors they are going to check you of course.

An implant in the hand should be simple: if your hand triggers the metal detector it is easy to verify that your hand is empty and that the location matches the documentation. Small magnet probably doesn't even trigger it though.

for a non-medical implant like this, though, you probably wouldn't be able to get official documentation. I'd hope that sense would prevail and it wouldn't be an issue, but good sense doesn't always govern airport security procedures, particularly in the US.