methods of communication

[D.G.]

No: HPFGUIDX 68816

Interesting question, and --most likely-- yet another of 
those "tidbits" dropped which will be revealed as vitally important 
later on.  

To postulate:  it's obvious that Wizards (or at least their Ministry) 
can keep track of magickal goings-on on a pretty continuous basis -- 
witness how easily they can ferret out Harry's unauthorized used of 
spells and charms when he's at the Dursleys'.  Maybe they've got some 
kind of spell-formulated tracking system; perhaps whether certain 
Wizards might be endowed with a form of mental communication even 
more immediate and accurate than Legilimency/Occlumency (something 
along the lines of what we Muggles might call "telepathy").  

They're probably forbidden to use it unless the circumstances are 
particularly dire.  But it seems clear that at least some of them can 
obviously "see" things from great distances, and it doesn't take too 
much of a stretch of the imagination to suppose that they can monitor 
others' thoughts and feelings from great distances, as well.

I'm guessing that something along these lines is what Dumbledore was 
referring to.  Perhaps by "reliable" he meant "quick and efficient," 
more than "not prone to breaking down."

D.G. ("JazzmanChgo")