Some rules background
There is a general rego vim guideline to create a spell container (p.161). In the core book this is used for Watching Ward/ Waiting spell. The description tells us that because of Watching Ward's potentially unlimited duration it must be a ritual. Rival Magic goes further and tells us that using a trigger to set off a spell contained within a container spell requires a ritual, (setting up the possible advancement from integrating Augustinian Magic). The spell Patient Spell from Magi of Hermes shows us that, using the core book guideline, a spell container can set off a spell at the end of its duration without any ritual involved.
I was, earlier today, thinking that it would be handy for a magus or maga to know when their ward against [Stuff] has been compromised. One way to do this was as follows:
Cast your circular ward against demons or whatever.
Then, on the same circle, cast the following
Ward of the Broken Circle
R: Touch, D; Ring, T: Ind.
Ward of the Broken Circle Places another spell or spells on hold until the Ward of the Broken Circle ends, typically when the ring that is used for Ward of the Broken Circle is, itself, broken. When Ward of the Broken circle ends the suspended spells take effect as if they were cast. Spells so released are not necessarily meaningfully targeted. The storyguide should determine the manner in which these spells go off if there is any uncertainty.
Ward of the Broken Circle can contain spells with a total level up to two magnitudes higher than the level of Ward of the Broken Circle. Only one Ward of the Broken circle can be placed on any one physical circle.
(General, +1 Touch, +2 Ring)
The restriction to just one ward of the Broken Circle spell being placed in any one circle is from watching ward but I'm not at all sure that it's essential.
I suspect the simplest such alarm would be a momentary Creo Imaginem spell that makes an alarm noise. That's base one. At range touch duration momentary it's only level 2. (Is momentary long enough to say, "Holy Poop! the demon ward went down!"? I think it is.) You'll need an extra magnitude for understandable speech If you add another magnitude to make it as loud as 10 people you are still only at level 4. That means your Ward of the Broken Circle can be level 2. Both of these can be sponted by characters who have arts at 0.
If you've got more horsepower to run your spells you can have a silent alarm
Alert of the failed Ward
R: Arcane Connection, D: Momentary, Target Individual
This spell creates a set of words in the mind of the target ed individual, such as, for instance, "Warning, ward in sector G7 has failed.". The spell is cast with an arcane connection
(Base 3, +4 Arcane Connection)
If you want that spell to target you, you'll need to leave your own AC in the circle and cast it with enough moxie to penetrate your own parma.
This still only requires a level 5 version of Ward of the Broken Circle, which is good because you'd hardly want to leave an AC to yourself lying around. So you'd couple it with a perdo Corpus base 3 range touch to destroy the AC. That means your ward of the Broken Circle can still be level 10, But you'd still be safer to have your spell target a grog. Leaving an AC to your person lying around is just asking for trouble.
A different choice, if your Ward Against Demons is located within a room, is to store a target room version of Demon's Eternal Oblivion.
But say you'd like to set off a whole slew of stored spells all at once, yes, they could be low level high penetration versions of the target room demon's eternal oblivion spell, but they could also each produce 100 cubic paces of lava leading to a lava tsumami. or they could each create a flock of owls or, if you are really esoteric, you could set off a suite of muto spells to change each type of target in the room (herbam, ignem, animal, vim, etc) into the smell of freshly baked bread.
To do that, you make a whole series of concentric circles. You put a Ward of the Broken Circle on each of them with a spell you want to set off in your bunch in it, Then, make an outermost circle and within it store a perdo or rego effect to mess with the floor and break all of the inner circles (it wouldn't need to be perdo or rego there are lots of ways to break circles).
Obviously there doesn't need to be a circular ward against [stuff] involved, that's just how the idea first came to me.