The long range sensors (also called deep space sensors) are sensors situated in Atlantis, which can detect things with a portion of the Pegasus galaxy, including ships moving in hyperspace (amongst the only sensors known to be able to do so.) The exact range the sensors cover is unknown, but the area it covers can give Atlantis up to three weeks advanced warning of the approach of Wraith Hive Ships travelling far beyond the speed of light. Other space faring races, such the Asurans (who use older Lantean sensors,) can give up to a day's warning. Rodney McKay was able to modify the sensors to locate the subspace frequency used by Wraith trackers. (SGA: "The Brotherhood", "The Siege", " Sateda", "The Return, Part 1")