How does a Wizard becoming 'untraceable'?

[kiricat2001]

No: HPFGUIDX 105134

--- In HPforGrownups at yahoogroups.com, "Jen Reese" <stevejjen at e...> 
wrote:
> According to the FAQ on JKR's website, a witch or wizard can become 
> untraceable just like a building can be unplottable. JKR said this 
> in response to the question of why the MOM didn't send an owl to 
> Sirius and follow it.
> 
> Any ideas? It must tie in with Dumbledore in PS, when he said there 
> are other ways to become invisible besides using an Invisibility 
> cloak. 
> 
> Maybe there's nothing more to it, just another complex spell in the 
> WW that we haven't heard about yet!


Marianne:

I wonder if this will turn out to be an explanation that only leads 
to more questions.  How complicated is this? How much time does it 
take?  Do you need a wand to do this? If you're untraceable, can 
people see you when you're standing right next to them?  

I'd think the answer to the last question has to be "Yes" otherwise 
there would be no need for a Secret Keeper to hide James' and Lily's 
location.  They could have simply wandered about in untraceable 
bliss.  Unless once they each were untraceable, they couldn't find 
each other. And,Sirius would not have had to stay shut inside 12 
Grimmauld Place for nine months.

So, I don't think it necessarily makes one invisible. I think it 
means that whatever methods wizards use to establish or reach the 
location of a person who is at some distance away don't work.  They 
can't lock on to their target (even if the target is simply someone 
to whom you're sending a birthday card) because the target can't be 
traced.

Marianne