Perception

Your Wisdom (Perception) Skill Check lets you spot, hear, or otherwise detect the presence of something. It measures your general awareness of your surroundings and the keenness of your senses. For example, you might try to hear a conversation through a closed door, eavesdrop under an open window, or hear monsters moving stealthily in the forest. Or you might try to spot things that are obscured or easy to miss, whether they are orcs lying in ambush on a road, thugs hiding in the shadows of an alley, or candlelight under a closed secret door.

Perception Ranges

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Perceiving Spellcasting

Many spells create obvious effects: explosions of fire, walls of ice, teleportation, etc. The effects of these spells are visible at a range determined by the size of the effect, audible at a distance determined by the volume of the noise effect of the spell, and subject to a Wisdom (Perception) check by anyone within sensory range of the effect. (Situational modifiers are listed below.)
Other spells, such as Charm Person, display little visible, audible, or otherwise perceptible sign of their effects, and could easily go unnoticed even at close range. However, characters could still perceive the spellcasting process itself. Unless a character attempts to cast a spell subtly, it is assumed that all creatures in the vicinity will notice the casting.
When you attempt to cast a spell with subtlety, you must make a Dexterity (Sleight of Hand) check. If other characters in the vicinity are not watching closely, then the check is made opposed by the passive perception of the creature with the highest Wisdom (Perception) ability in the area. The DC of the check is modified by the situational modifiers below, at the discretion of the GM.
If other characters in the spellcaster’s vicinity are watching the spellcaster closely or are on alert, then the Dexterity (Sleight of Hand) check is contested by a Wisdom (Perception) check rolled by that creature. The creature attempting to perceive the spell receives a bonus to its roll equal to the rank of the spell being cast, as well as situational modifiers below at the discretion of the GM.
If the spell has been mastered, then the caster gets Advantage on his or her Dexterity (Sleight of Hand) check in either case, and the situational modifiers are ignored.
Any creature damaged by a spell automatically perceives it.
The following modifiers may apply, at the discretion of the GM. The total perception modifier is listed on each spell's stat block.
Casting Perception modifiers:

• +1 if it has a somatic component
• +2 if it has a verbal component
• +3 if it has a material component
• Additional +1 to +10 if there are sensory signatures during casting

Effect Perception modifiers:

• +1 if there is a visible or audible effect that manifests in a small area on the caster (tiny visual / no audio)
• +2 if there is a visible or audible effect that surrounding the caster but limited to his/her person (small visual / very quiet)
• +5 if there is a visible or audible effect that affects a 5-foot square (medium visual / quiet)
• +8 if there is a visible or audible effect that affects a 5-foot radius circle, sphere or cylinder, or a 10-foot cube, or multiple creatures within a range. (large visual / moderate audio)
• +10 if there is a visible or audible effect that affects up to a 30-foot radius circle, sphere, or cylinder, or a 60-foot cube, or a massive number of creatures within that range, or a large cone. (huge visual / loud audio)
• +12 if there is a visible or audible effect that is larger than 60 feet. (gargantuan visual / very loud audio )