A peep hole is a small opening, typically found in doors, that allows a person to see who is outside without opening the door. It is often fitted with a lens to provide a wider view, enhancing security by enabling homeowners to identify visitors before granting access. Peep holes are commonly used in residential settings, but they can also be found in commercial buildings. They serve as a simple yet effective security measure, helping to prevent unwanted entry and ensuring the safety of individuals inside. Many modern doors come with pre-installed peep holes for added convenience.