This is an antique brass door knocker with an integrated peephole viewer, often referred to as a "speakeasy" or door viewer knocker.  These knockers served a dual purpose as a traditional knocker for visitors to announce their presence and a peephole or "viewer" that allowed occupants to safely see who is at the door before opening it.

These integrated units were particularly popular in the early 20th century, specifically the 1920s and later, and are associated with architectural styles like Art Deco, Gothic Revival, or Provincial.  They are typically made from durable materials like brass, cast iron, or zinc alloy, and can come in various finishes such as antique brass, polished brass, or oil-rubbed bronze. The design of this item is a classic or Provincial style.

This unit has a brass patina finish and is very heavy.  When I hold a magnet to it there is the slightest bit of magnetism indicating that it is not a solid brass.  This item is likely an alloy containing small amounts of other metals.