It’s Canon Now: Detect Magic CAN (sorta) Detect Invisibility, plus a small revision to the Interacting with Illusions rule
Now you guys are aware of my house rules re Illusions in general – visual (plus other senses as per the caster) illusions that only provoke a will save only at the point they are interacted with, and then only evaporate for the individual making the will save, with bonuses to the save if they’ve been made aware by others that the image may be an illusions (typically +2).
But that doesn’t necessarily address all instances of Detect Magic and how it interacts with Invisibility and illusions – basically, deceptive magic. In earlier games, Detect Magic could be (and would be) used as a the poor man’s See Invisibility or Detect Illusion – if someone suspected either of these spells were being used, they could fire up a cone of Detect Magic and voila! Problems solved. Obviously this was not the intended use of that spell, especially since it was so low level compared to the spells it was effectively negating.
In later editions, we find the spell See Invisibility showing up, the presence and level (2nd, equivalent to Invisibility’s 2nd level) of which in itself implies that 0-level Detect Magic is insufficient to locate Invisibles.
But here’s the thing – a review of research says that, yes, Detect Magic CAN detect invisible creatures and/or objects… just not very well. From the Paizo boards:
Range 60 ft.
Area cone-shaped emanation
You detect magical auras. The amount of information revealed depends on
how long you study a particular area or subject.
1st Round: Presence or absence of magical auras.
2nd Round: Number of different magical auras and the power of the most potent aura.
3rd Round: The strength and location of each aura. If the items or creatures bearing the auras are in line of sight, you can make Knowledge (arcana) skill checks to determine the school of magic involved in each. (Make one check per aura: DC 15 + spell level, or 15 + 1/2 caster level for a nonspell effect.)
So –
Round 1: You cast the spell and learn “there’s magic someplace within my 60′ cone-shaped emanation”
Round 2: “there x number of magics”
Round 3: “one of them I can’t see but it’s in that square, and I think it’s of the illusion school”
But if the invisible thing moves out of the your cone-shaped emanation, you have to begin studying a new area to try to re-aquire it, meaning you have to start all over again at step 1.
Ok, makes sense BUT:
Detect Magic picks up ALL magic auras, so if one of your party members is standing in front of you with 5 magic items, you get 5 magic auras + all of the magic auras from the invisible person. So round 2 you get X magic auras, and you need to pick a single one to focus on. You do not know the location until you spend another round concentrating on that aura, so it is very possible that you would spends 3 rounds examining an aura only to find out it is the fighters +2 magic sword.
Sometimes, it is enough to get the info from round 1. Round 1, Wizard casts detect magic. Round 2, wizard moves in front of partly , they check to see if they still detect magic (move action), they cast cone of cold (which hits roughly the same area as detect magic).
Etc etc. The forums go on like this for absolute pages. But one thing struck me – in a lot of the discussion, Invisibility was treated – at least somewhat – like an illusion. So my proposal for Canon:
- Detect Magic does have the potential to detect a creature using Invisibility BUT
- It follows the params of the Detect Magic spell as outlined:
1st Round: Presence or absence of magical auras. [basically, a yes or no question for the entire 60′ cone]
2nd Round: Number of different magical auras and the power of the most potent aura. [a number and a strength: “there are six auras and the strongest is moderate”]
3rd Round: The strength and location of each aura. If the items or creatures bearing the auras are in line of sight, you can make Knowledge (arcana) skill checks to determine the school of magic involved in each. (Make one check per aura: DC 15 + spell level, or 15 + 1/2 caster level for a nonspell effect.) If the aura emanates from a magic item, you can attempt to identify its properties (see Spellcraft).
That’s the rub right there for Invisibility – if it’s in line of site, you can do a Knowledge Arcana on it and determine it’s of the Illusion school. It’s not pinpoint accuracy, but it will give the other casters in the party the option to cast Glitterdust, Dispel magic, AoE spells, etc.
Which leads me back to our current rule about illusions – you interact with them to get a Will save to disbelieve, but not before. As an addendum to that and based on the above, I would say that Detect Magic is effectively interacting with an illusion (IF it is recognized as an illusion) and therefore provokes a will save to disbelieve.
