A Trap Detector is a special type of item exclusive to the ScareScraper mode of Luigi's Mansion 3. It is a small, red, glowing siren which is attached to Luigi's head. After finding one, any player may equip it - once equipped, the siren remains with the player until the floor is cleared.
If a player is in possession of a Trap Detector, they are made aware of any traps they come in proximity of, such as fake carpets, doors, and wardrobes. As the player nears a trap, the sounds made by the siren become louder and faster, while its lights grow larger. This is helpful for avoiding traps as well as destroying them for a sum of treasure.
Trap Detectors are rare items, usually only found in invisible objects and furniture which must be revealed with the Dark-Light Device and examined. If the player finds a hidden treasure room on a floor, they may enter to find a treasure chest in the center of the room containing a Trap Detector along with all the other special items, which may be distributed to the players.