The Exclusion of Aegis Sodalis
Intellego Corpus (Vim) 20
R: Personal, D: Momentary, T: Structure
Provides the exact locations of any individuals within the structure that have not participated in the caster's Aegis of the Hearth. This spell only works if the caster is within an Aegis of the Hearth where he or she was a participant.
(Base: 5 "Sense a specific piece of information about a body." +3 Structure)
Nice idea. A good way of finding people in the structure who were not party to the Aegis. This of course counts as scrying...
But I doubt that you will really care at this stage.
A
Since the Aegis does not differ between a participant of the ritual casting and someone who carries a token, I take it that visiting magi who are carrying a token would not be detected by this spell either.
But that won't give any info about the interloper hiding in the bushes outside the building you're casting it on...of course, a similar spell with Target: Boundary would itself be a ritual...oh, and with a form of 'corpus' you won't spot non-humans either. Why not make it Vim only? Your spell could then be used to spot any target (small 't') that hadn't participated in the Aegis.
However, I would definitely require either two magnitudes adding in to represent the complexity of what you want to do (as written, it is the same exact level as a spell to just detect any humans within the structure, but you want to distinguish between humans who should be present and those who should not be) or an extremely high finesse roll. And that presumes no magical attempt to hide being made by the interlopers.
I might suggest an alternative method/spell: InVi, to 'interrogate' the Aegis spell directly rather than to target the individuals who might be within a structure, thus avoiding both the hiding in the bushes problem AND the not-corpus one. I'm not sure what level to make this - it's not the same as 'talking to' the Aegis, since the Aegis has no ability to detect interlopers; rather, it's a spell so you can see where the 'swirls of magical power' from the Aegis are behaving differently to normal. Even someone who is invisible should (unless they are expecting this method of detection) show up this way. And, as Buddha says, it won't distinguish between tokeneers and original participants.
Base 5: detect any active magic (I think that, while an Aegis is likely to be higher enough magnitude that you could use a lower base (Base 1-4), this spell would be detecting subtle aspects of that spell, not merely its presence - avoiding needing complexity magnitudes?)
That would be L40 - now, will it need any extra magnitudes for complexity? (I presume you'd want to avoid this being a ritual?)
What do you all think?
Edit: since you are only affecting your own sense of sight, to see the swirls of magic that are already present, you won't be 'pinging' anyone's parma. Scrying? Yes, but very hard to prove that you've done it!
Of course this would detect all of the grogs and covenfolk too - kind of a pain....
Seems reasonable. Remember though that just having physical possession of a casting token isn't enough to nullify the Aegis; it has to have been bestowed explicitly by a participant of the Aegis, and the nullification can be revoked at any instant, even without taking the token back. So this "loophole" doesn't seem very big at all.
This would detect creatures with Might - but not (most) magi, which seems like a pretty big design flaw, depending on what you're paranoid about. :mrgreen:
This is a cool creative idea, but I don't think this is how it works. Creatures with Might, or foreign magi, are totally allowed to walk around inside an Aegis all they want (if they can get in in the first place). Once they're inside, the Aegis doesn't do anything to them other than make it harder for them to cause supernatural effects (powers or spells). So if a foreigner is inside the Aegis but not currently using any supernatural powers, I don't see why the Aegis's "swirls" would notice them at all.
ArM5 p.161 col.3:
The proposed spell certainly would not detect most covenant members. If there were any new members for that year since Aegis of the Hearth was case, you would detect them, but you want to keep an eye on them anyway.
I was thinking that current invites would not be located.
I felt certain that participation in the ritual was a property of the body, with "power" (therefore the Vim requisite), and therefore could reasonably be checked. As for checking the Aegis itself, I was vastly less sure about that.
As for Might-based supernatural beings, as long as they have a "human-like" body (a great many), they're affected. After all, I can cast Curse of Circe on a faerie or demon. If they're animals or spirits, then not. I suppose it may depend on what your personal definition of human-like is. Mine is pretty broad.
You wouldn't want to detect animals as all the sheep, goats, dogs, chickens, horses, cows, rats, mice, pigeons, and bugs possibly living in the covenant; that would make it useless.
No, it detects the Aegis directly and how that interacts with whatever you are looking at. (As an aside, InVi can detect magi - their highest Art counts the same as the Might score of a creature (divide each by 5 to get the effective magnitude) - but does need a specific spell, rather than one that detects Might.)
The Aegis has a differing effect on non-participants vs participants. If you don't like the word 'swirls', then use a different one - the magic is all over the warded area, and it 'does stuff' to non-participants. How does it do that? We don't know, but I think it is reasonable for my spell to show how the Aegis is interacting with people. The argument about 'currently using their powers' is valid, but that has to apply to whatever method is used to detect them.
Sense of the Lingering Magic might show the residues of the Aegis, but again doesn't need to be corpus. You'd need an alternative spell to that one though because it just shows if there is ANY lingering magic on someone. And the SG might rule that actually, the Aegis was cast onto the area warded - the participants weren't the targets, after all.
Well, not having thought about this before, I wasn't sure about how to go about it either 
I like my version - it's high level, so only decent magi will be able to use it (which explains why it isn't in common usage already) and it would only pick up on any of those animals if the caster were looking at them at the time.
My reasoning was that the original spell suggested wouldn't do what you wanted - it would simply detect every human present. And it would need to penetrate everyone's MR. Mine is based on Sight of the Active Magics - the original detects any active spell effects and identifies the techniques and forms involved. This spell is specifically tailored to detecting how an Aegis is interacting with people and others. A SG might rule that this spell only shows them up when they are actively using powers/magic that are hindered by the Aegis, but I think that is unnecessary because if they didn't want you to be able to do this at all, they should tell you, and this is already nearly a ritual due to the high level - and if they did make that rule, it would also affect any alternative method of detecting them.
Anyway, have fun whatever version of this you use.
Source? I know you can use InVi to detect the Gift, but that's scrying. As would the above be, obviously.
p158, AM5 core rules, in the notes below the InVi guidelines. Yes, definitely scrying, as is the spell that Rain of Steel wants in this topic.
You're absolutely right, I'd missed that line.
Excellent!