robertsconley
Adventurer
I want to highlight a portion of the OP that may clarify @pemerton's point of view.I know I'm late to this so maybe this has already been answered, but... how would the intruders (a) know an alarm spell had been set and (b) know the spell's duration?
Presumably, the intruders would have to watch the caster casting the spell and make an Arcana check, and be stealthier than the entire party's passive or active Perception (or the equivalent in a different system) and continue to beat their Perceptions for the entire eight hours. That's a lot to just accept.
It's possible, in TB2e, for a wily intruder to avoid the alarm, but that would be a narration adopted after the camp event roll is made and an unhappy event results despite the bonus. And it is possible for the watch to be too distracted or drowsy or whatever to effectively respond, despite the alarm; but again, that would be a narration adopted after their test to avert disaster fails, notwithstanding the +1D bonus.
What is happening is the party has camped, a series of rolls are made, then a narrative is crafted to fit the results generated by the rolls. From my experience with these types of mechanics, elements of the narrative would have been created as the rolls were being made. But the final "story" of the event with elements of who, what, and why is only created afterwards.
I hope that help with understanding what the differences are.