Gem Finder

The Gem Finder is an item that can be purchased from Professor E. Gadd's Shopping Network for 1,000G in Luigi's Mansion 3. Once bought, it reveals the location of one gem on the player's map.

Luigi's Mansion 3 description
E. Gadd's Shopping Network: "That's a cartridge that'll project the location of a gem on your map. Each one reveals the location of one gem!"