I saw some of a movie with one of the baldwins, he was an assasin that used a modified rifle to shoot a *very* small projectile, needle like. He shoots this guy in the neck, he swats like it was a bee-sting, then he collapses from a "heart attack".
And this was either after or right before reading something off internet/noble realms about how they do this in real life, "cause" heart attacks to happen. I notice this happens a lot, finding material that is "confirmed" from some obscure movie/television plot, that by chance I happen to have seen.
Truth is stranger then fiction...
Cell phones shooting tracking nodes doesn't seem too far-fetched. Except that most people have a cell already, which is good enough for tracking. The implant's must carry another function...