Okay, something has been bothering me for a while, and I thought it's about time I get some input from here.
To be activated by mental command a magic item needs an appropriate InMe effect to read thoughts continually. According to ArM5, p.99 this would be:
15 Base (read surface thoughts)
+1 Touch range
+1 Concentration duration
+5 levels for the item to maintain concentration
... for a total of 30. Given the enchantment rules though, this has several drawbacks.
The mental command effect has to have a physical trigger itself.
If left to its own devices, the item's concentration fizzles at sunrise or sunset.
If the former happens, the item is done for the day - it has no additional uses per day.
It has to penetrate Magic Resistance.
It is a Touch range effect with Concentration duration. Given my understanding of Hermetic magic this means it can only affect one target per casting whose thoughts it can read as long as it maintains concentration, regardless of the range to the target afterwards.
So in order to fix (most of) these problems, I set out to come up with this effect:
15 Base (read surface thoughts)
+2 Sun duration
+1 Touch target
+4 levels constant effect (environmental trigger, 2 uses per day)
For a total of 34. Close enough to the book suggestion and it actually allows the item to continually read the thoughts of those that touch it.
This isn't really a problem, since the physical trigger can be nearly any action. Putting on a ring or crown, buckling a belt, pinning a cloak pin, even simply touching the item are valid.
Yes, these are problems.
Not precisely a problem, IMO, since a magus can lower his resistance by a simple act of will, and the act of performing the simple physical action to activate an item shouldn't even require a Concentration roll.
To me, this sounds less like a bug and more like a feature.
Indeed, the continuous effect has always seemed a better solution to me, for the same reasons you mention.
It can be either. But given the standard expectations for "mental trigger" are not "the first person to touch this object in a day can henceforth activate it by thought, no matter if they separated afterwards", it's a bug in this regard. In respect to Magic Resistance it's a feature, since as an innate magical sense it would have to penetrate Magic Resistance continually, while as written it only has to penetrate once during activation.
Nonetheless, the high level is still frustrating. It's likely that this is one of the more standard lab texts in Hermetic libraries, but for enchanting talismans lab texts do little good. So I've been thinking if this could be reduced further in that respect.
15 Base
+2 Sun
+4 levels constant effect
For a total of 29. The talisman only has to read its owner's thoughts, to which it has Personal range as long as they are touching anyway, so no magic sense is necessary. This also means that it doesn't have to penetrate your Magic Resistance, since it's a Personal range effect. So no lowering of the Parma necessary.
Er.... That would allow the device to read the mind of whomever touched it at sunrise/sunset, for the rest of the day.
Just add multiple uses, with the "device touched" trigger.
Sounds good. I generally dislike mental triggers due to warping, but this could help bypass the problem in a few ways as well as working as intended but more in line with the rules.
In respect to Magic Resistance it's a feature, since as an innate magical sense it would have to penetrate Magic Resistance continually, while as written it only has to penetrate once during activation.