Forum:Konoha Detection System

In Manga Chapter 419, there is a Detection sphere placed around Konoha. It is used to show where and when a intruder is getting into Konoha. Should we put this as a Jutsu or put it into the Konohagakure section? I know it is small but I would like to know. If it is already put in as a Jutsu, could someone tell me? I am sorry for using this for such a small detail but I thought it would be worth some thought. -Juubi no Ryuu