Long range sensors
Three Hive Ships on Atlantis' long range sensors
Production information
Manufacturer	Ancients
Technical specifications
Function	Long range sensors
Usage
Affiliation	Ancients Tau'ri

[Source]

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 traveling far beyond the speed of light. Rodney McKay was able to modify the sensors to locate the subspace frequency used by Wraith trackers. (ATL: "The Brotherhood", "The Siege, Part 3", "Sateda", "The Return, Part 1")