This reminds me an old James Bond movie, with Sean Connery, where he picks one of his hair, licks his sticky fingers to seal his hotel room door. It later tells him that someone entered his room.
Depends on the author.
Some authors are well-known for the thoroughness of their research. Some spy novels have been so accurate that ex-intelligence people have approached the authors to ask them how they knew certain things, and to offer them more information that would be useful for new manuscripts.