Wizard/Muggle "Radar"

[Kristen]

No: HPFGUIDX 108764

Earlier posts speculated about whether Molly might be a weakness in 
the OOtP, so I was wondering where Arthur's vulnerabilities might 
lie . . . 

This got me thinking:  could a wizard "pass" as a muggle to fool 
another wizard?  (Without the use of some kind of "hiding" spell on 
the one's part, or Legilimency on the other's; also disregarding for 
now the possibility of repressed magical powers as has been 
speculated of Petunia or Dudley.)  

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?