Are there rules for detecting if someone is casting a spell outside of combat? Is it merely a Perception check of some sort?
Are there feats to improve one's ability to cast undetected?
My bard is interested in casting spells when dealing with NPC's--not Charm or Enchantment spells, per se; the spell would most likely be cast on himself. For example, could he cast
Eagle's Splendor* without being noticed by a small crowd of neutral townsfolk?
*Verbal, Somatic, and Material components required to cast.
There is no mechanical rule to detect if somebody is casting a spell outside of combat. But the movements of casting a spell are typically interupted that the person is doing something abnormal or mystical.
The only "rules" that accomidate this are those listed under Componets:
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Components
A spell's
components explain what you must do or possess to cast the spell. The
components entry in a spell description includes abbreviations that tell you what type of
components it requires. Specifics for material and focus
components are given at the end of the descriptive text. Usually you don't need to worry about
components, but when you can't use a component for some reason or when a material or focus component is expensive, then the
components are important.
Verbal (V)
A verbal component is a spoken incantation. To provide a verbal component, you must be able to speak in a strong voice. A
silence spell or a gag spoils the incantation (and thus the spell). a spellcaster who has been
deafened has a 20% chance of spoiling any spell with a verbal component that he tries to cast.
Somatic (S)
A somatic component is a measured and precise movement of the hand. You must have at least one hand free to provide a somatic component.
Material (M)
A material component consists of one or more physical substances or objects that are annihilated by the spell energies in the casting process. Unless a cost is given for a material component, the cost is negligible. Don't bother to keep track of material
components with negligible cost. Assume you have all you need as long as you have your spell component pouch.
Focus (F)
A focus component is a prop of some sort. Unlike a material component, a focus is not consumed when the spell is cast and can be reused. As with material
components, the cost for a focus is negligible unless a price is given. Assume that focus
components of negligible cost are in your spell component pouch.
Divine Focus (DF)
A divine focus component is an item of spiritual significance. The divine focus for a
cleric or a
paladin is a holy symbol appropriate to the character's faith. The divine focus for a
druid or a ranger is a sprig of holly, or some other sacred plant.
If the
Components line includes F/DF or M/DF, the arcane version of the spell has a focus component or a material component (the abbreviation before the slash) and the divine version has a divine focus component (the abbreviation after the slash).
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As to what degree these mean, you would have to ask your DM.
There are feats that can remove these components: Still Spell, Silent Spell & Eshew Materials.
Again talk with your DM, but unless it is against the law, how big a deal it would be to cast a spell in public.