Perception checks through a familiar's eyes

Question

If I cast the find familiar spell and summon a familiar, then I can look through my familiar's eyes, hear through its ears, and communicate with it telepathically. (It is not a blind or deaf creature. If the question of whether it can understand my thoughts is an issue, then assume I am a warlock and my familiar is an imp.)

I tell the familiar to stop for a moment so I can make an active effort to concentrate on what I see and hear. Therefore, I roll a Perception check.

Do I roll it with the familiar's perception modifier, or my own modifier? Or one roll for me and one roll for the familiar?

Answer 1

You both roll.

Perception is a skill, not a sense. Two people see exactly the same thing, and one of them notices a small detail or something out of place that the other does not notice. (Sherlock Holmes: "You see, but you do not observe. The distinction is clear.") When your own perception skill increases with more levels, it is not because you magically grow a better pair of eyes. You learn how better to utilize whatever eyes you are looking through.

You and your familiar are two different creatures looking at the same picture. You both can apply your observational skills to that picture and tell each other what you notice.

Answer 2

Rulings and rules. Three cases, each with its own rationale. Part two of the question asks (potentially) about rolling twice for the same perception check, which could be handled via Advantage to a roll. (p.4 Basic Rules).

1. Do I roll it with the familiar's perception modifier, or my own modifier?
2. Or one roll for me and one roll for the familiar?

1. Conservative ruling: You character's total range of perception and understanding is what informs your actions and reactions.

   Use your Wisdom, because what your familiar is adding are enhanced sensory inputs and thoughts to your ability to understand various sensory clues, and arrive at what it is you are seeing, feeling, smelling, hearing, etc.

2. Alternate ruling: I get by with a little help from my friends

   Include the wisdom/mental processes of your intelligent familiar. From the spell description for Find Familiar:

   In combat, it rolls its own initiative and acts on its own turn. A familiar can’t attack, but it can take other actions as normal.

   You get Advantage on the perception roll by you choosing a familiar's action. Core point is that the familiar is using the Help Action to give you Advantage. In this case, you don't actually roll his and yours, but yours twice. Does this apply out of combat? Sure, why not! (See Discussion).

3. The third path: Whomever hears or sees better feeds the decision process

   Make one check, but use the higher wisdom / perception bonus between you to reflect best sensory and cognitive fusion. Apply Advantage (thus two rolls) if one party uses the Help action for the other. If your familiar has a better wisdom or proficiency than you on the particular check, huzzah.

   Notes:
   a. Alternate ruling addressed part 2 of the question.
   b. The third path addressed the revised question, part 1.

4. Discussion.

   a. Per RAW (Basic, p. 57-65) Perception takes sensory inputs and via mental processing arrives at an understanding of what is seen, heard, smelled, felt, surmised, etc.

   p. 62:

   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.

   b. Whether you are looking through your eyes or hearing with your ears, or feeling with your fingers or the extremities of your familiar, your Perception check's success is based on your wisdom.

5. Support for the Alternate ruling?

   Include the wisdom/mental processes of your intelligent familiar as an additional enhancement.

   a. There's a valid game mechanics reason to go with Advantage. You make perception checks at Advantage when using a Familiar if it takes the Help action.

   b. Why shouldn't you get the benefit of your familiar's brain? It's in addition to yours! He's helping you, so you should have advantage! Even if you are both using his senses mostly, perception is tied to Wisdom and your familiar has a Wisdom score.

   c. See Working Together for non-combat situations. If he can take a Help action in combat, no reason not to be able to help out of combat. (Two heads are better than one, and not just for Death Dogs!).

   p.59:

   Working Together
   Sometimes two or more characters team up to attempt a task. The character who’s leading the effort—or the one with the highest ability modifier—can make an ability check with advantage, reflecting the help provided by the other characters. In combat, this requires the Help action (see chapter 9).

   p. 72:

   Help
   You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains advantage on the next ability check it makes to perform the task you are helping with, provided that it makes the check before the start of your next turn.

6. Support for the third path

   Make one check, but use the higher wisdom / perception bonus between you to reflect sensory and cognitive fusion.

   Roll using the best bonuses between you to reflect getting the benefit of the familiar's senses and reasoning as well as yours. Your familiar is a reasoning/intelligent sensor, not just better eyes or ears. Roll twice (Advantage) if the other party takes the help action, in combat or out.

Answer 3

There are a number of options for you to consider:

Your familiar is helping you to search

You have asked your familiar to assist you, by staying still, holding their head steady, focusing on some thing, etc. Mechanically the familiar used the Help action on their turn:

You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains advantage on the next ability check it makes to perform the task you are helping with, provided that it makes the check before the start of your next turn.

Both of you search

Alternately, you could just tell your familiar that you want to search for something, in which case on their turn they can take the Search action too.

When you take the Search action, you devote your attention to finding something. Depending on the nature of your search, the DM might have you make a Wisdom (Perception) check or an Intelligence (Investigation) check.

Mechanically these two options are very similar. You still end up rolling 2 die for perception, but with the former you make both the rolls, with the later you make one and your familiar makes one. But the later has the advantage of you being able to do something else if your familiar succeeds on the check.

You could also forego telling your familiar to stop, and try your luck with a straight search check:

Using Help

• On your turn: "Hey familiar, stop there, I want to take a closer look at that"
• On your familiars turn: Stops, takes the Help action
• On your following turn: See through your familiars eyes as an action, as another action use Search, roll Perception with Advantage.

Using Search

• On your turn: "Hey familiar, let's take a closer look over there"
• On your familiars turn: Stops, takes the Search action
• On your following turn: See through your familiars eyes as an action, as another action use Search, roll as normal

Using neither

• On your turn: See through your familiars eyes as an action, as another action use Search, roll as normal

You need 2 actions on the same turn to attempt this

Find familiar states:

as an action, you can see through your familiar's eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the familiar has

Making skill checks takes an action in combat, and there is even a special action called Search for making perception checks.

You need to use one action to see through your familiar's eyes, and another to Search. However seeing through your familiars eyes only lasts until the start of your next turn, so you don't have enough actions to make this happen.

Currently there is no way to get Search as a bonus action, so I'm not sure exactly how you plan to pull this off. But you could use action surge or something similar.