I've seen a number of passengers express amazement that they got through the detector without alarming -- even though they have implants. Invariably, it seems, when I ask these passengers how old their implants are, they report 10 years or older.

It's been my experience that passengers with newer implants (under 10 years) seem to set off the class of metal detectors now in use. It's just a theory, but I think after a number of years, the tissue of the recipient somehow shields the implant from detection. I would like to see someone conduct a formal study of this -- I'd do it myself but the management dullards I work with freak out if I merely pull out a notebook and jot a quick note.