[RPG] Does perception rely on sight or hearing

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When you are heavily obstructed and someone tries to hide from you, can you find out his location by hearing? What is the range of your passive perception based on hearing?

Best Answer

A Perception check can rely on any sense, and your DM decides what is appropriate for the situation.

Perception represents how perceptive a character is in all their senses, not just sight or hearing (from the SRD):

Perception. Your Wisdom (Perception) 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.

Which sense is used with your passive Perception score or when making a Perception check depends on the sense being used. Even though that will usually be vision (often enough that people tend to assume Perception is always about vision), the situation may call for the use of another sense. You may have advantage, disadvantage, or neither on your passive Perception score or Perception check for a particular sense.

Consider the following mastiff feature to see an example where this differentiation appears in the rules (see Player's Handbook page 307, and note for sake of contrast that many other beasts in the PHB, SRD, and Monster Manual include similar Keen [Sense] features):

Keen Hearing and Smell. The mastiff has advantage on Wisdom (Perception) checks that rely on hearing or smell.

This makes sense because dogs have excellent hearing and sense of smell but do not have very good eyesight. Conversely, humans have exceptional eyesight but only average hearing and very poor sense of smell. In the scenario you've given, since heavy obstruction generally completely blocks sight, you may try to use your hearing to locate a creature behind the obstruction, but the DM will have to determine whether the situation is favorable or unfavorable.

Since humanoids are much less adept at hearing than sight, if the DM decides that you can or will make a Perception check based on hearing, they might require you to make the check with disadvantage if they think circumstances are disadvantageous for you to be able to identify the location of the creature by hearing. And if you were to try to identify the location of a creature by smelling their odor or identify the location of a humanoid by sniffing their cologne as it drifts by, the DM would almost definitely rule you to be at a disadvantage.

So, the short answer to your question is: your passive Perception score is as high as the DM rules it to be for a particular scenario using a particular sense. By default, your Passive perception score is 10 + your Perception modifier, but if you have advantage in the case of a particular sense then it is increased by +5, or if you have disadvantage then it is decreased by -5, and your DM adjudicates what is appropriate.

For example, if your Perception modifier is +3, then you generally have passive Perception 13, but you might have have passive Perception 18 if the DM believes that the situation is in your favor for a particular sense or 8 if they believe you are seriously limited in your ability to succeed in perceiving something with that particular sense.

Note that Perception can not allow you to perceive something it is impossible to perceive. If a creature is hidden from view, completely silent, and without odor or other telltale signs such as shadows affecting the area, the DM may rule that it is completely impossible for you to detect them. In that case, a Perception check is not called for because you only roll an ability check when there is a possibility of success, and you would automatically fail on passive Perception as well.

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