The Room of Requirement

[Beth]

No: HPFGUIDX 68576

During the DA's first practice, the Dark Detectors are mentioned 
twice, once when Harry first spies them, and once when Dean asks 
about them. And while Harry explains that "you don't want to rely on 
them too much," the Foe-glass, at least, revealed Fake!Moody's 
enemies in GoF. So why don't any of the Dark Detectors go off before 
Dobby comes to warn the DA's of Umbridge's approach?

Also, if the room merely summons, rather than creates, aren't 
Flitwick, Pince, et al annoyed when their possession disappear? 
(Maybe that's what's happening to Luna's stuff--someone has need of 
it <g>)

Beth