The description of this spell is wrong. However, there is very little information about it online, and the little there is, is quite contradictory. The best I've found is the page about the spell in the wiki, but the wiki tends to be quite unreliable. Can anybody confirm what the spell actually does?
To avoid confusion I want to emphasize that, as the title and this first post say, this thread is about the Non-detection SPELL. It is NOT about the Non-detection cloak. Information about the cloak is welcome, of course, but is not the main topic of the thread.