Perception skills have had a long tradition of being used to sense incoming bandits, find loot, sometimes to find traps and even to find secret passageways. It becomes an invaluable skill in order to further the plot and to keep yourself alive. Oftentimes, GM’s will call for Perception rolls like calling Initiative, with all players stopping the role-playing flow to roll dice to determine outcome creating a giant metaphorical flashing neon sign saying “Plot and Items exist here!”.
When to call for Perception Rolls
The best time to ask an entire group for a perception roll is: Never, it only serves to disrupt game flow! Any agency, tension, tone, or flow that Roleplaying requires is quickly lost when players hear a GM say “Roll for <insert anything here>”. Any group that happens to get off-topic knows how detrimental losing the flow of dialogue can take on a game. Group perception rolls slow down the game. It will remove the players from any immersion they have in a scene, or when flowing between scenes. Perception should only be asked of players when their characters are specifically doing something that would require a perception check. As an example, when the group enters a new room this should not require a perception roll; however, when the rouge wishes to find a good place to hide in the new room, this should require a roll by the player.
Before each session, the GM should ask for a series of rolls from the players (around 20 to be safe) which should be placed in whichever order they wish. These items should be written on a piece of paper like an index card with bonuses for skills like perception/empathy/search/investigate. Sure many systems have a “Passive version” of skills (which is normally a static number based on the average roll), but this will be a static number. The only problem with a static number is it makes difficulty checks useless. When a GM has a difficulty that is higher than the passive version of a skill, these characters will not notice what would benefit them, otherwise, they will notice. In this case, the GM will know the result before the characters are even in the scene. Pre-rolling allows this to become more randomized and allows characters with low perception to notice things sometimes, as opposed to only having the character with the highest perception be the only one to notice anything out of the blue.
Pre-Rolling and Player Uncertainty
One strength in pre-rolling and not having players know the results, you can create a challenge within the campaign by giving some players conflicting information. A perfect example of this would be empathy checks to determine if a Non-Player Character is lying. by pre-rolling results, a GM can let one player know that their character believes a statement to be a lie, where another could believe it to be true. Without knowing the results of their own roll, the players will have to ask further questions, or perhaps roll another check (because in this case, they are actively searching) to determine the true outcome. Conflicting information can provide quite a lot of depth and play without a lot of work for the GM. Score!
What Perception Rolls should uncover when they are rolled
The plot should never be dependant on Perception Rolls. This doesn’t mean that the outcome of perception is irrelevant to the plot; it should not depend on a perception roll to advance. In terms of plot development, perception should be used as a “degree of success” as opposed to Pass/Fail. No matter what, the plot should keep developing and not be allowed to stagnate. In the event that a party rolls abysmally, this should not stop the story from progressing; instead creating an additional or alternate scene in order to continue.
As an example, a party is hunting for an attempted assassin. While investigating, one player is tasked with searching the would-be assassin’s previous living quarters. If the player rolls well, they might immediately find a secret passage. Rolling poorly may have them instead uncover an item with distinct markings, like a pendant. A Game Master would be able to indicate that the character knows someone who may be able to get them more information on the item. Meeting with that character would give the player the information that it belongs to a member of an assassin’s guild that is known for using secret passageways, leading them to the passageway that they missed previously.
Personally, if the players roll well enough (like a Natural 20), I like to have clues uncovered by the Shaggy Search Technique. Rolling really low, such as a Natural 1, will likely have a similar result, but also put the character in immediate danger. Zoinks!
Perception Rolls will always be a large part of RPGs when outcomes must be determined by rolls, but in terms of story and plot, some of the pass/fail of perception rolls needs to change. However, where Active rolls are concerned, not much really needs to change. These problems do not apply to Active Rolls that are based on actions that characters have taken. They really only apply when the Game Master would ask for a roll that is unprompted by character action. However, it can be fun for everyone if the outcome is unknown to the player too.