While I agree with OneShot, I'll note that some canon examples are technically backward. The reason I say this is that with MuVi in an item, it should be the MuVi firing off and then what it's affecting would be linked to it. But there is at least one example written backward.
I would have thought the base spell would have to trigger the MuVi spell, since there's no target to 'Muto' until the spell is being triggered. It's like saying 'My opponent might summon a horse, I should PeAn in preparation'.
This made me double check the rules for MuVi (p159 by the way) and the actual answer is the spells need to be cast at the same time, rather than one after the other. There's some fun interpretation of someone trying to say "Creo Ignem and Muto Vim!" at the same time, but I think the logical expectation is that the there's a moment where the spells form in the caster's mind and will (soul?) and the gestures and words impose that upon reality and the airy spirits. Either way, the rules that MuVi spells have to be fast-cast suggests that either spell can be the trigger and the other will jump in to help. Of course, you don't have a choice to cast both at once with that.
@StephenFleetwood I'm curious what you were thinking at for the original item. A wand that you wave, and wards just pop onto the weilder, one after the other? I think you could actually just make it so that 2-3 spells have the same activation triggers.
@raccoonmask I was thinking something that put up, say a ward vs steel, then a ward vs mundane animals, then a ward vs fire, then a ward vs creatures with might. Basically a broad range set of protective powers for someone to trigger at the start of a problem and then forget about the item.
Well, the rules say you can instill multiple effects to a single trigger, though I didn't see evidence that only one spell goes off a round that way. I think that they all go off on the same round for protection.
So a single activation can be the trigger for multiple effects, which all go off simultaneously.
If the activation only triggers one effect, which in turn triggers another, and so on, I would expect the effects to not go off simultaneously. Since the Hermetic 'clock tick' is Mom, I would expect at least that much time to elapse between effects that cascade in this way.
So we can have a device with three effects, the first a teleportation effect that teleports the device to a place the magus specifies (and to which he has an AC) during activation, the second an effect that creates a giant fireball and is triggered by the first effect going off, and a third effect that returns the device to the magus triggered by the second effect has gone off. Ok, maybe a fourth effect, to make the device extremely resistant to fire.
Of course, if the magus has an AC to some location, he can learn a fireball spell at AC range and just cast that. Or create a fireball item using AC range.