Hotel detective
A hotel detective is a plain clothes person engaged to monitor the security of a hotel and investigate various security or rule violations therein -- not the same as uniformed security guards employed by a hotel.
Description
Hotel detectives were often retired or ex-police officers with some training and feature prominently in certain noir fiction, especially in the works of Raymond Chandler, and are sometimes referred to as "House Dicks". The term "hotel detective" is no longer widely used, as most hotels now employ uniformed security staff who leave any investigations to law enforcement agencies.