Siege Auspices are powerful scanners that can see through the densest materials to find their weak points. These items are used for finding stress fractures, reinforced or up-armoured areas, hidden passages, power conduits, and the numerous other items of interest to a siege engineer. The machine-spirits of a siege auspex, while canny, can only see so far through solid objects and have a fixed range of about 20 metres. Things like energy fields, thick bulkheads, iron, stone, armaplas, and plasteel can reduce the range of the unit or blind it altogether.
- Deathwatch: Rites of Battle, pg. 146