I guess you understood what is this all about from the name title...
Its a gadget that officers use before proceeding with their mission..They place it over the peephole in the door and look into the domicile.
source
Features:
- High quality lightweight materials.
- Housing is strong, lightweight, and weather resistant.
- Lenses are custom designed, high-quality, precision
ground glass.- Designed to be carried by all types of officers.
- Simple to use.
- Can be carried a on web belt, on a vest, or in a pocket. Comes with carrying
pouch.