Regarding the effect modification "environmental trigger" (Ars5, page 99)...
In the core rulebook, the events that can, well, trigger an environmental trigger are limited to "major magical features of the environment." Major magical features of the environment are, themselves, pretty much limited to:
events that can end spell durations, and
changes in the aura modifier.
In various other 5th edition products, however, environmental trigger seems to be used much more broadly. Case in point, "The Crystal of a Hundred Candles" in Guardians of the Forest triggers based on opening a door, while the "Fire Guardian" in the Semita Errabunda sample covenant triggers based on the existence of a fire in the covenant library.
Do I misunderstand "environmental trigger," or is this an inconsistency in the published material?
Page 99 says "The feature is triggered by some feature of the items environment rather than a specific action. the item is only sensitive to major magical features of te environment. Thus it can respond to the events that end spell durations and to changes in the modifier..."
Clearly environmental triggers are not limited to only those two things. yet as they are the provided examples of "major magical features" you'd think that opening or closing a door wouldn't work.
Yet breaking a circle might.
From page 98 we can get an understanding of a triggereing action "A trigger can involve a command word or phrase, moving the item in a specific way, a stanfe to be adopted or anythng physical that you can imagine...by default the trigger action must be performed by someone holgngte item"
So free triggering actions have a lot more leeway than the +3 level environmental trigger.
I'd be tempted to interpret "major magical features" extremly broadly seeing as it's harder to do than "anything physical than you can imagine".
So yes I think it is an inconsistancy in the published material. But since we are players rather than the publisher I'd be tempted to go with the Semita Errabunda, and Guardians of the Forrest examples than a restrictive reading of page 99
I would rather conclude that the authors of the examples mixed up linked triggers (where Intellego effects can detect changes in an item's environment) and environmental triggers, and forgot to develop and incorporate the needed Intellego effects.
This ArM5 distinction of linked and environmental triggers makes a lot of sense for me - even if its wording makes its application from memory error prone. It requires that a magus designs how an item detects environmental changes, unless spells could react to such changes already on their own.
Lumping both kinds of triggers together can be exploited with cheap devices attaching a complex and free detection mechanism to a trivial effect. Want - for example - to be sure when going to bed that your covenant is secured? Just design a nice D:Diam CrIm 2 fanfare pseudo-environmentally triggered every nightfall if there is still a gate, door or window in your covenant open or unlocked.