Star Trek: Technical Difficulties Unexplained

I just finished watching a DVD of one of my favorite Star Trek original series episodes ... "A Piece of the Action." A planetary society builds its entire framework after the Chicago mobs of the 1920's, all because of a book on that subject is left behind by an earlier Federation ship.

http://www.treknation.com/episodes/tos/season2/a_piece_of_the_action.shtml

The story is pure camp, but I love the dialog and the acting of Anthony Caruso as Bela Oxmyx and Vic Tayback as Jojo Krako.

Now, here's the topic thread ... Star Trek never tried to fully explain away all things in the show. For instance, how exactly did they maintain gravity in a ship where no rotational structure was present? (As opposed to, for instance, the ship "Discovery" in 2001: A Space Odyssey.)

So here's a new topic thread ... what are some other "technical difficulties unexplained" in the original Star Trek episodes? I'll start ...

Personnel Location Devices

The Enterprise was a very sophisticated ship. The Federation had very sophisticated technology. Why is it, then, they did not have each member of the crew embedded with a location device so that when they got into a jam they could just be transported away? Episode after episode a crew member somehow worked their way into jeopardy where a simple transport back to the ship would have solved the problem ... but they couldn't locate the person to beam 'em back. Their Tricorders and Communicators were small devices, so clearly they had the ability to construct small things. Why not, then, an implated beacon device?