I am interested in hearing your opinions on the matter, does a magus or a maga realise that he or she is a victim of comprehend magic? For those who doesn’t know about comprehend magic it’s a phenomena from HoH:Soc.
Thanks for your thoughts
/MAx
IMO, no, no more than he would notice someone watching him with sense holiness/unholiness. He may notive someone is watching him strangely, but that's all.
Gotta sleep, i'm dead beat
I'm not familiar with the comprehend magic ability so I may be talking nonsense here. I think that the question is whether or not comprehend magic neds to penetrate in order to work. All supernatural abilities have a penetration score. If there is isn't one specifically stated in the ability write up they should use the sytem defined in the core rules book.
If comprehend magic is a passive thing that doesn't need to penetrate then I don't see how the observed magi could sense it. If comprehend magic is an active thing then magi could feel it pinging their parma if they resist.
Greetings,
In short, it's described as passive scrutiny, or analysis (sic) of active magic. Hence, to my mind it should imply a no penetration sense.
Yet, as written, there might be some contradictions, or room for speculation at least. First, for characters who'd like to acquire further knowledge than the basic "presence of magic" sense, it is specified that :
(* : emphasis, mine).
So, on one hand it's described as a passive sense for "active magic/ongoing effets", on the other hand it seems to become an active "power" when the character tries to further inspect whatever magical onion he's analysing.
Needlessly complicated, imho, but well. 
So, to answer the OP question, I guess that being superficially tested by Comprehend Magic is not something one can detect. And that perhaps one could sense further observation... As I read it, anyway, even though I don't like this and would probably not
Oh, and as a side but not so unrelated note about this ability...
I'm also slightly bothered by the paragraph about "Pralicians and Scrying", which, in short, states that Comprehend Magic is considered as magical scrying, and that a character who used it to pursue more information about another magus "than the bare minimum"(sic), risk to be convicted of a High Crime... provided that the prosecuting side proves that a Pralician gained more than basic recognition of his Gift.
Even if I consider that some Guernicus could probably hold such severe view against Comprehend Magic because of its defiance of the Pralixians motives and way, it's clearly a far-fetched argument, from surprisingly heavy handed Quaesitores... no less than would be the same accusation held against a magus who'd just used his own training in the Arts to recognize another magus's spell in casting.
Well, that was long enough for my very first post here, I guess. 8)
If it needs to Penetrate, as you mention in that quote, then it's going to set off the Parma radar. Frankly though, as a player of a very security conscious and fairly paranoid magus, I don't want you comprehending me-- it's scrying, plain and simple. If you suspect I'm a magus, try talking to me. I have to speak latin to belong to the Order, and chances are you can frame a question that clarifies the matter without whipping out the old supernatural abilities and giving me the crazy eye. That's the sort of thing that can get you in a Certamen...
And saying "Oh, but I was just using my lineage's gift...I meant no harm." doesn't cut it. Is the magus using some enhanced sense to subtly observe my magus? Welcome to Scry-town, population: you.
Is it an interesting ability with a lot of potential, sure is. I won't argue that. But don't point it at a someone just to see if they're a magus; you could easily end up with more than you bargained for.
-Ben.
Hi,
Comprehend Magic does require Penetration, but what the section is intended to say is that even if it does not penetrate the user can detect the presence of magic. Penetration is required for the additional rounds of scrutiny that provide additional benefit, such as type of magic, function of magic, and magnitude.
To answer the original question - the viewed person is aware that he has been scryed if the effect fails to Penetrate (see Awareness of Attack, ArM5, page 85). This applies to all Magic Resistance, not just Parma. Since Penetration for Comprehend Magic will be pretty poor, the chances are that parma will stop it and you'll have a charge of scrying to deal with.
I would also draw your attention to the insert which specifically addresses the issue of scrying. It quite baldly states (first sentence):
...and then goes on to state that tribunals are often lenient about the simple detection of magic. However, if a 'victim' pushed the issue, it is de facto Code-breaking. Don't forget, however, that (paranoid individuals aside) Code-breaking doesn't always lead to punishment - someone has to bring up charges, and you may be able to work things out with the person you've just scryed. On the other hand, you've just committed a High Crime, and thus forfieted the immunity of the Code...Leonis is right - speak to people first!
Cheers,
Mark