EDIT: As a side note, this where as a DM I would have suggested that those players with the Arcana skill, make a roll and given them the opportunity for them to "know" the magical theory that I was operating under, with a successful roll I would say "Remembering back to some of your earlier lessons, you remember that magical alarms do not work on visual cues, but on magical divinations and a simple illusion is unlikely to bypass it".
I believe that as a low level spell, Alarm doesn't have the power to determine anything for itself. It can't magically sense Dwarves and Wizards. Otherwise you could use it as a detector for anything. The conditions "people who didn't try and kill me last night", or the condition "People who aren't plotting to overthrow the king" would allow the PCs to work out any secret with a single low level spell.
What defines a Wizard? Belonging to the class? What about multi-class characters? What about someone with the Magic Initiate feat?
I don't think the spell should have any extra-ordinarily powerful divination magics to determine if it goes off. Straight up visual sensing seems far more appropriate. I've interpreted the clause "designate targets who don't set it off" as people you know and can name (not theoretical groups of people: vegans, pessimists, politicians) . And I'd say that without any magical senses a disguise of any sort would fool it.
Alternately, If you prefer a magical sense I would still explicitly require them to state the individuals who don't set off the alarm, and their magical signature gets read and ignored. In this case, I'd allow Nystul's Magic Aura to bypass it.
At the end of the day it is open to interpretation. I just think by allowing phrases like "wizard" to bypass it you're asking for a headache.
I believe that as a low level spell, Alarm doesn't have the power to determine anything for itself. It can't magically sense Dwarves and Wizards. Otherwise you could use it as a detector for anything. The conditions "people who didn't try and kill me last night", or the condition "People who aren't plotting to overthrow the king" would allow the PCs to work out any secret with a single low level spell.
What defines a Wizard? Belonging to the class? What about multi-class characters? What about someone with the Magic Initiate feat?
I don't think the spell should have any extra-ordinarily powerful divination magics to determine if it goes off. Straight up visual sensing seems far more appropriate. I've interpreted the clause "designate targets who don't set it off" as people you know and can name (not theoretical groups of people: vegans, pessimists, politicians) . And I'd say that without any magical senses a disguise of any sort would fool it.
Alternately, If you prefer a magical sense I would still explicitly require them to state the individuals who don't set off the alarm, and their magical signature gets read and ignored. In this case, I'd allow Nystul's Magic Aura to bypass it.
At the end of the day it is open to interpretation. I just think by allowing phrases like "wizard" to bypass it you're asking for a headache.
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