Wizard/Muggle "Radar"

[justcarol67]

No: HPFGUIDX 109092

> Kristen wrote:
<snip>
> In other words, if a (convincingly attired) witch or wizard walked 
> up to Arthur and said, "Hi, I'm Joe/Jane Muggle and I need your 
> help," would any magical "radar" alert the Arthur that things are 
> not what they seem?
> 
> 
> SSSusan responded:
<snip>  That's interesting--IS there any kind 
> of "wizard detecting" or "muggle detecting" ability inherent in 
> witches & wizards?  Not that I'm aware of.  But did I miss something 
> in the books?  Is this something Aurors are capable of?
> 
> Anybody have thoughts on this?

Carol adds:
Draco seems certain in GoF that the DEs who are tormenting the Muggle
Roberts family will instantly recognize Hermione as a Muggleborn and
subject her to the same treatment, so I think some such "radar" does
exist, only maybe in the opposite way to what Kristen is suggesting.
If that's the case, Arthur (or any pureblood) could presumably detect
a Muggle posing as a witch or wizard (not that such a thing is likely
to happen) because his "Muggle sensor" would be activated. If a witch
or wizard were posing as a Muggle, he'd be suspicious because he
*didn't* sense the presence of a Muggle.

It also seems that Tom Riddle could identify the Muggleborns at
Hogwarts even in Diary!Tom form, and evidently the basilisk could,
too. And yet it seems likely that this radar doesn't extend to
Half-bloods, since Tom himself probably passed as a pureblood at
Hogwarts, making sure that his Slytherin friends knew nothing of the
Muggle orphanage he returned to every summer.

Carol, who has wondered how the DEs would know that Hermione is a
Muggleborn and is glad that Kristen raised this point