Reverse Peephole Viewer
This little spy gadget lets you spy on the spy. The reverse peephole viewer let’s you look through a peephole in the wrong direction.
The reverse peephole viewer was designed for law enforcement officers so that they can check what’s behind a door without alerting the occupants though I’m sure any budding wannabe spy will find a use for it.
You can get the reverse peephole viewer from Spy Gadgets (found via Book of Joe)