Using these probes, mages (and sorceresses) can detect magical anomalies. 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 centre of the cemetery.
- The second must be placed in the relief directly outside of the sewer 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.