Sky-spy

 was Dalek technology which protected Skaro and was housed in the Daleks' capital city. It allowed the Daleks to detect incoming enemy vessels, and then to launch a deadly counter-attacks. It was therefore the primary target of the first ADF raid against Skaro, and was successfully destroyed by Joel Shaw, Reb Shavron and Mark Seven. (DWA: Terror Task Force)

It was unknown how long the system was in place, or when it was first put into service.