There are many different shapes and sizes of Medic Alert bracelets/necklaces.  When I was younger, I had a necklace.  It was very discreet, hardly noticeable really.  Currently I have a bracelet that essentially looks no different than an ID bracelet.  Aside from the small "charm" that serves as the Medic Alert, it is completely inconspicuous.  If anyone asks him, he can say"It’s my ID bracelet."