I'm tinkering with an item that will be invested with an effect that will be triggered by being touched by someone who is protected by an Aegis of the Hearth (or, alternately, someone who isn't).
My gut tells me that this would be an Intellego Vim to detect that protection, but I'm not sure what the guideline would be. Nothing in the core book's guidelines feels right; looking at the Spell Guidelines .pdf, I see Level 10: "Detect an active magic and any trace of positive magnitude" (Houses of Hermes: True Lineages p.74) and "Detect the Gift" (Hedge Magic p.6 and Apprentices p.33). Does this seem close enough to what I'm describing? If not, what would my esteemed sodales suggest?
Defining this more precisely might help you. Is a Grog protected by the Aegis because the power of a specific Faerie outside of the Aegis cannot penetrate it and affect him? Even if there is no such Faerie currently attempting to do this? Aegis boundaries are felt as a slight tingle by magical persons and Hermetic magi: so for this the knowledgeable do not need magic.
EDIT: To determine whether an enchanted item is activated within an Aegis of the Hearth, this effect within the item might do: InVi circa 25 (Base 5, detect whether ReVi +2, further detect whether Aegis circa +1, +1 Touch) [ArM5 p.158 box].
Depending on how you rule activation of enchanted devices within an Aegis IYC, in a 'foreign' Aegis this effect in the item might not work at all, need some solid penetration built in, or just work. Some Himinis out for ideas here?
The item was within the covenant's Aegis when it was cast, so it is unaffected. But I'm going with the interpretation that a foreign item's effect must have a penetration > ½ Aegis level to work.
And what I'm looking for is a "triggering" effect so that a second effect (e.g. opening a door or not smiting you) is based on whether the target either participated in the current casting or has a Casting token.
For example, if put in a door. If someone touches the door, it would trigger the effect in question, and if it determines that the person does have the Aegis's protection, the door would open; if not, it won't.
Hitching items' triggers into the workings of an Aegis risks running into problems with the last paragraph of the Aegis' description (ArM5 p.161) and hence requiring a major breakthrough. Couldn't you establish in your covenant a convention about tokens for the Aegis, and have the enchanted devices look for tokens of a specific type instead?
So e. g. everybody participating at the Aegis' ritual at your covenant, and everybody invited into it later, gets a leaf from the oak at the covenant square (or a mushroom from a specific fungus in the central dungeon) containing a pawn of Herbam vis as a token for the Aegis, which is collected and renewed every year at winter solstice. And your protective magic items need to be touched with that type of token (i. e. oak leave/mushroom not older than a year, from a specific tree/fungus, and with 1 pawn of Herbam vis in it) or respond aggressively.
On second thoughts, that is exactly what a small (say, level 20) Watching Ward (ArM5 p. 162) with trigger condition "opening the door" and known to the magi of the covenant accomplishes, if every covenant member has learned a ReVi 20 suppression spell (R: Touch, D: Mom, T: Ind) for magic of level 20 or less cast by another (ArM5 p.161 box).
They open the door immediately after having cast the spell, so the Ward is suppressed during that moment. Casting the suppression spell is easy for those with just Re 5 and Vi 5 - so magi having time and leisure for such defenses are not hampered. But with a solid Aegis (say, level 40 - as Semita Errabunda has it) subtracting from the casting totals, an uninvited magus, even if he knows of the Ward and has a fitting suppression spell, will need a solid ReVi casting total (30 in case of Semita Errabunda) to bypass it.
First detecting and then dispelling the Ward with general purpose standard spells like InVi 40 Sight of the Active Magics (ArM5 p. 159) and PeVi 30+ Wind of Mundane Silence (ArM5 p. 161) is quite impossible unless the uninvited magus is a master of Vim or has lots of vis, and hence might just bring down your level 40 Aegis with a specialized PeVi 25 spell (R: Touch, D: Mom, T: Ind) to dispel Hermetic Vim magic (ArM5 p.160 box) for starters.
We ruled that an effect within an aegis had to penetrate after we (not any opponent: we, our characters) used a CrIg boundary item with zero penetration to burn down a rival covenant when we were at wizard's war with them. We even hurt the magi there, since the flames were mundane after the item had gone off and the covenant was in flames. We used to use that item to clear fields of stubs before planting. Turning that into a bomb was so silly for us that we replayed the session with the items being unable to work unless their penetration was equal to the aegis level. It screwed some of our own items we were using in the aegis (Less than a year since we bought them), but in general it worked better.