Geralt receives three of these magic sensors from Triss Merigold at beginning of Chapter III. They each must be placed in a specific location in order to triangulate on the coordinates of the magical anomaly.
- One must be placed inside the "relief" on the back of the remaining standing wall of the ruined church in the center of the cemetery.
- The second must be placed in the relief directly outside of the Vizima sewers entrance in the Temple Quarter, which is down the stairs outside the Detective's house.
- The third relief is located on the wall outside the bank, behind the town hall in the Trade Quarter.