I have 2 metal plates in my right forearm, I have since I was 12yrs old and NEVER EVER has it gone off in an airport security scan. The first few times I flew I took x-rays etc to prove it but after NEVER having been stopped I didnt bother taking documents.
I have a metal pin pointer that will react to my plates and my ground search metal detector goes nuts near my arm but NEVER, even in a manual metal detecting sweep, has it ever been detected in an airport.