 Dr. McCoys handheld "medical scanners" were actually modified salt  and pepper shakers, purchased originally for use in the episode "The  Man Trap", in which a character was seen using a salt shaker. They  were of Scandinavian design, and on screen were not recognizable as  salt shakers; so a few generic salt shakers were borrowed from the  studio commissary, and the "futuristic" looking shakers became  McCoys medical instruments.