Peep Hole Reverser

“Peep hole reverser was developed with the help of the law enforcement industry to help them assess potential hazards behind dwelling doors. This peephole reverse viewer is simple to use and can be carried in your pocket for use anytime.
Just place the reverse viewer over the peephole in the door and you can look into the dwelling without alerting anyone inside. Spoooky”

Source: Spy Gadgets