Spy holes are small openings or peep holes that allow a person to observe an area without being seen. They are often used in doors, walls, or other structures to provide a discreet way to check for visitors or monitor surroundings. Spy holes can enhance security by allowing individuals to assess a situation before deciding to open a door or engage with someone. These openings can vary in size and design, with some being simple drilled holes and others featuring lenses for a wider view. Spy holes are commonly found in residential homes, security doors, and even military installations for surveillance purposes.