I went in to the doctor today for more x-rays, and I chatted with him a bit about the machines. He was pretty certain that the hardware will be picked up by the image scanners regardless (despite the fact that the machines shouldn't be able to see under the skin) and he seemed to think that when I am called for a secondary pat-down, it is because we are dealing with lesser-trained agents who don't recognize the hardware for what it is. His advice was to just show them the scar when they pull me aside

(just wanted to note - I will go through wave mm detectors, but not x-ray)