I'm having a few problems getting my head around devices casting spells.
Let us take the canonical example of the wand of bestial agony (ArM5 p97-100)
How does that wand know which Target to target?
I can see it is something of a point-and-click interface, but what happens if there are two animals very close together? If the wielder can still distinguish them is that fine?
What if it isn't a wand but a hat? Can an invested device with a linked trigger cast bestial agony on a valid target in range without the hat itself being able to perceive the animal?
Separate example, If we have a device that can cast Leap of homecoming, how does the device know where to leap to? I.e if the wielder possesses multiple objects all of which are themselves arcane connections to different places (not all of them fixed) does the device transport the wielder to any of them, or does it select one according to a rule I can't find?
My instinct is to say that if there is an active mind telling the device what to do and to whom, then the device itself does not need to perceive the target, but I cannot find evidence to support me. This means that unattended items are much less versatile (so no traps that can do fancy shenanigans) but I am OK with that.