Stealth Encounters

A Rogue moving quietly down a dimly lit passageway; a Wizard using Minor illusion to draw away a guard's attention; a disguised Bard moving unnoticed through a crowd; all of these are examples of stealth encounters. A stealth encounter is a type of encounter where players try to explore an environment or gain information without being noticed by enemies. Where the Hide action governs the use of stealth in combat, the following rules can be used for this type of non-combat situation.

Stealth Encounters

In a stealth encounter, the players must avoid drawing attention while completing their goals, such as stealing an item, gathering information, or reaching a certain location. Stealth encounters usually take place in some restricted location with a form of guards or other security. If they are caught, these guards may try to escort the players outside of the restricted area, raise an alarm, or even attack depending on their attitude or alignment.

When running a stealth encounter, it is usually a good idea to map out the restricted area they have to move through, and it may be helpful to use initiative when precise timing is required (such as avoiding a moving searchlight). When a player character wants to bypass some sort of security or perform a task without being noticed, they can use the Sneak Action, as detailed below. If multiple creatures are trying to Sneak together, you can have them make a group check. If at least half the group succeeds on this check, the whole group succeeds.

In general, a Sneak action is only required if a creature is attempting a new stealthy task. For example, you might ask your players to make a Dexterity (Stealth) check to move down a hall past some guards, a second check to avoid a searchlight, and a Dexterity (Sleight of Hand) check to retrieve a key from a guard's waist. However if your players have already succeeded on a check to move quietly past an obstacle, it's generally not a great idea to ask for another check as soon as they enter a new room or move past an identical obstacle, as that can greatly decrease your players' odds of maintaining sneakiness. Organizing individual elements of security into groups can help reduce the number of checks needed. Additionally, when your players fail a check to Sneak it can be good to embrace the idea of "failing forward." Rather than immediately breaking their cover and having guards rush to attack, you can rule that the players remain out of sight, but the guards become more suspicious.

Sneak

When you take the Sneak action, you attempt to avoid drawing attention while moving or doing some other task. The Sneak table suggest which ability checks to make based on how you're trying to be sneaky. The DM chooses the check, which has a default DC equal to 10 or the monster's Passive Perception (if the players are making a dexterity check) or passive Insight (if the players are making a Charisma check), whichever is Higher. You have advantage on a Dexterity check made to Sneak if you are Invisible.

Ability Check	Method of Sneaking
Charisma (Performance)	Using a disguise or making a distraction through acting.
Dexterity (Sleight of Hand)	Picking a Pocket, Throwing a noisemaker, or some other subtle or precise movement
Dexterity(Stealth)	Moving quietly and staying out of Sight.

Awareness

Each enemy creature within a restricted area has a certain level of awareness which can change depending on the players' actions and the result of their Sneak actions. Most creatures' awareness will start at Unaware, and become more aware as they witness suspicious activity.

Unaware

The creature is unaware of your presence and will act normally

Suspicious

The creature suspects something is amiss. An Unaware creature becomes Suspicious if they witness suspicious activity, such as a loud noise, an unexplained movement, a disguised creature behaving oddly, or a deactivated security measure. A Suspicious creature will investigate the suspicious activity, and become Unaware if they witness no further suspicious activity within the next 10 minutes.

Alarmed

The creature knows you are in the restricted area, even if they do not know your exact location. A Suspicious creature becomes Alarmed if they witness alarming activity, such as seeing an unobscured intruder, hearing an alarm, being attacked or forced to make a saving throw, discovering a dead guard, or witnessing at least three suspicious activities within a 10 minute time period. An Alarmed creature may continually search for intruders, raise an audible alarm, or confront the intruders if they can see them. An Alarmed creature becomes Unaware if they witness no further suspicious activity or alarming activity for 1 Hour.

Restricted Areas & Security

All stealth encounters hinge on the design of the restricted area the players must navigate through. A good restricted area has a mix of security measures to overcome, and hiding spots and vantages the players can use in that endeavor. Dimly lit alcoves, scalable walls and balconies, and conveniently placed tools can all help provide opportunities for your players and make the process of sneaking more engaging.

When designing your restricted area, consider which security measures you want to use to help set the tone of the encounter. Below are some common types of security that can be used to design a restricted area.

Alarms

Alarms are devices and magical wards used to alert the guards in a restricted area that an intruder is present. The most common type of alarms are bells stationed along walls or on a post in a courtyard. A bell can be disabled by removing its clapper through making a Dexterity (Sleight of Hand) Check.

In restricted areas with magical defenses, the Alarm Spell is another common type of alarm. These can be frustrating for players to encounter if there is no advanced warning, so try to find ways to telegraph the possibility of that spell (such as an obvious mage visible among the early guards or glyphs carved along the floor).

Guards

Guards are creatures tasked with detecting and apprehending intruders, such as standard humanoid soldiers, beasts trained for their keen senses, and tireless constructs and undead. Unaware guards will usually either stick to one area or patrol a small route. Their movements should generally follow a pattern that players can recognize and exploit if they watch carefully.

When choosing what monster stat blocks to use for guards, consider the tone you want to set and the ways you expect your players to deal with guards. If you want a tense encounter where being spotted could be fatal, choose tough-looking monsters with a CR appropriate for a Moderate or High difficulty combat. Alternatively, if you want guards to be disposable obstacles on their own, use low CR monster that could be killed in one attack with some higher CR monsters that won't cress paths with the players unless the alarm is raised.

Additionally, consider varying the behavior and skills of individual guards to add to the suspense. A relaxed yet Athletic guard might quickly clear obstacles to reach the party if an alarm is raised; a twitchy guard with a high Perception could prove especially difficult to bypass; an officer with high Insight may recognize that disguised creatures aren't supposed to be in that area.

Locked Doors

Locked doors, windows, and other barriers are a simple obstacle that can add another wrinkle to a stealth encounter. If your players don't have a means to pick the lock, they can search for a key held by a guard or try to force through the barrier at the risk of making noise. If they have Thieves' Tools, picking a lock is a fairly simple task but can be made more complicated with the addition of other security nearby. Remember the philosophy of failing forward when dealing with locked doors; if a player fails a check to pick a lock, consider having the door open after a longer time than anticipated or with a loud noise and suspicious noise.

Searchlights

If your stealth encounter is set at night or in a dark area, searchlights can be a great way to add tension in more open areas. Searchlights may be bonfires focused with lenses or mirrors into a beam, or a magical sphere of light controlled by a mage. Like guards, searchlights should generally move in a regular pattern until an intruder is caught in their light.

Traps

Traps can make for great security measures in restricted areas like a cultist's temple or a kobold's den. The activation of a trap could create enough noise to draw a guard's attention and make them suspicious, and traps that focus on immobilizing intruders (such as a falling net) can add tension when combined with other security like a moving searchlight. Additionally, traps can provide great opportunities for players to distract or disable guards through clever timing.

Facing

While situations like combat don't normally call for dedicated facing rules, when running guards in a stealth encounter it may be useful to track their facing. A guard can see in a cone in front of whichever direction they are facing, and can change their facing whenever they move, or as a Reaction to hearing suspicious or alarming activity. A guard will usually face in the direction which they are moving.