[RPG] What information do creatures passively gain from constant “Detect” spells


Consider the Night Hag. The Night Hag has "constant detect chaos, detect evil, detect good, detect law, and detect magic."

However, each spell reveals additional information for each round "you study a particular area or subject." Detect Magic, for example:

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.) If the aura emanates from a magic item, you can attempt to identify its properties (see

Would a rogue wearing magic items be able to sneak up on an inattentive Night Hag? (Assuming his Stealth is sufficient.)

Unlike continuous True Seeing, which is entirely passive, Detect spells seem to need to be activated. In other words, does a creature with continuous Detect Magic need to consciously choose to begin using the ability before it has any effect? If not, how do you handle the fact that the area of the spell is a cone, and not a radius? And if so, what is the difference between "continuous" Detect Magic and using it "at will"?

(Unless something in Pathfinder overrules it, D&D 3.5e answers are good too.)

Best Answer

Since all of the Detect spells have a duration of Concentration, it seems to me like you have to concentrate to gain a benefit from them. If the Night Hag concentrates for 1 round, she can use any of her detect spells without having to cast it, but she doesn't get any information without concentrating. The difference here between continuous and at will is that the continuous version doesn't provoke an attack of opportunity. I don't think there's a solid rule on this, but I feel like this solution fits the normal behavior of the spells best.

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