Guide

Recipes#

Each recipe is a few steps and a reason. They link to the page that explains the feature in full.

Detection#

Hear footsteps#

Make a Sound Type Definition data asset, DA_Sound_Footstep: Base Loudness 1, Max Range 800.
Add an anim notify named Footstep to your walk and run animations.
In the player Blueprint: AnimNotify_Footstep → Emit Sound (Source: Self, Sound Type: DA_Sound_Footstep).
The AI's profile needs Hearing Sense in Sense Classes (it's there by default).

Why: APS never makes sounds from movement. The AI hears exactly what your game emits, nothing else. Hearing

Make sprinting louder than walking#

A second asset, DA_Sound_Sprint (Base Loudness 1.8, Max Range 1600, Alert Level Loud), and branch in the same notify:

AnimNotify_Footstep
  └─► Get Velocity → Vector Length → Branch: > 450
        True  → Emit Sound (DA_Sound_Sprint)
        False → Emit Sound (DA_Sound_Footstep)

Add a quiet DA_Sound_Crouch (Base Loudness 0.3, Max Range 300, Alert Level Whisper) for crouched steps and you have three tiers of movement stealth.

Stop it seeing through doors, vehicles and other pawns#

Profile › Detection › Occlusion › Vision Occlusion Channels: list every channel that should block sight. The list replaces Visibility, so add Visibility too if your walls block that. Empty means Visibility only.
Bodies blocking sight: tick Pawns Block Sight.
Check the geometry really blocks that channel in its collision settings.

Why: Unreal's perception tests one channel, so props on a custom channel are see-through to it. Each extra channel is one more trace per point: add only what you need. Senses

Let foliage and smoke hide you partly#

Profile › Detection › Occlusion › Surface Vision Transmission: SurfaceType_Glass 1, SurfaceType_Foliage 0.4, SurfaceType_Smoke 0.15 (your own physical surfaces).

Why: the value is the share of sight that gets through; anything not listed blocks completely. A player in tall grass is partly seen, not all or nothing. Confidence

Make crouching hide the player#

On the player, an APS Target Component with Auto Detect Stance ticked (the default).
Profile › Detection › Visibility: Min Visible Points Crouched 2, Min Visible Points Prone 3.

Why: all three are 1 by default, so adding the component never makes anyone harder to see. At 2, a crouched player behind cover must show two points before it counts at all. Confidence

Make its sight follow its head#

Profile › Detection › Eyes: Use Eye Socket on, Eye Socket Name head, Eye Direction Mode Socket Rotation (head bone), Eye Socket Alignment Automatic (the default), Eye Turn Rate Deg Per Sec 200.

Why: Automatic reads the skeleton's rest pose, so a plain bone name works on any rig. The turn rate stops the cone snapping to a Move To target before the body has turned. Senses

Make a dark corner dark#

At Begin Play: Get APS Subsystem → Set Sun Direction (your directional light's forward vector).
Profile › Detection › Light: tick Use Per Target Light (Trace Sun Shadow is on already; Shadow Light Level 0.25).
Optional, exact: set Light Level Override on the player's APS Target Component from your own light gem. It wins whatever the profile says.

World & fairness

Fairness#

Give the player a beat to duck back#

Profile › Fairness › First Spot Reaction Time 0.4. Until the AI first suspects a target, it must see it this long before confidence counts. World & fairness

Warn before it commits#

Profile › Fairness › Telegraph Threshold 0.22 (between Suspect and Detect), then:

On AI Telegraph (Target, Confidence)
  ├─► play "Hm?"
  ├─► Set Focus (Target)          // the head turns
  └─► flash a pip on the HUD

It fires once per target, and again only after the AI has let that target go. World & fairness

Give the player a safe room#

Safe room, Begin Play: Get APS Subsystem → Register Never Search Zone (Center: Get Actor Location, Radius: 600).
Then honour it, this part is required: before sending the AI anywhere (On AI Lost, each search point), ask Is Location in Never Search Zone on its APS Core; true means don't go.

APS doesn't enforce zones by itself. Search & evidence

Searching#

Investigate a noise without dropping a chase#

On AI Hear (Location, Loudness, Sound Type Name)
  └─► Branch: Blackboard HasTarget is false AND Sound Type Name is not None
        True → Blackboard InvestigateLocation = Location

Without HasTarget, every distant footstep interrupts a pursuit. Without the None check, the updates between sounds (the build-up) move the spot to where the player is now. Hearing

Search the corner it lost you behind#

On AI Lost (Target, Last Known, Predicted, Last Cover Actor)
  └─► Blackboard
        ├─ LastKnownPosition = Last Known
        ├─ LastCoverActor    = Last Cover Actor
        ├─ LossReason        = Get Loss Reason (Target)
        ├─ LossDirection     = Get Loss Direction (Target)
        └─ SearchRadius      = Get Uncertainty Radius (Target)

Then branch the tree on LossReason (Behavior Trees). Last Cover Actor is the object it traced against when it lost you: flanking that is the biggest perceived-intelligence win there is. Memory

Search wider the longer you hide#

Use APS Search: Begin Search at the last known position, then Get Best Search Point until Is Search Exhausted. It searches where you could have got to, avoids walls, and clears as it walks. Search & evidence

Without it: move to Get Random Reachable Point in Radius around LastKnownPosition with Radius = Get Uncertainty Radius. The radius grows at Uncertainty Growth Rate while you're lost, up to Max Uncertainty Radius, and, with Velocity Scaled Uncertainty (on by default), up to 3 times faster for a target that was moving fast (1800 cm/s or more).

Make it search longer before giving up#

Profile › Memory › Min Time in Lost 8 (25 for a horror stalker). A target can't leave Lost for Remembered until it has been Lost this long, however far confidence has fallen. It is the "how stubborn" dial.

Reactions and UI#

A detection meter#

Get Belief Data (Player) → Break → Smoothed Confidence, 0 to 1, in a widget's tick or a 0.1 s timer.

The APS Core has variables named Smoothed Confidence and Current State. APS 3.0 never updates them (0 and Unaware always). Read the belief about your target instead.

In multiplayer perception runs on the server: see Multiplayer.

React to seeing differently from hearing#

On AI Detect (Target, Threat Level, Stimulus)
  └─► Switch on Stimulus
        ├─ Vision       → engage
        ├─ Hearing      → go and look, weapon lowered
        ├─ Smell        → follow the trail
        ├─ Damage       → take cover first, then look
        ├─ Shared Intel → approach carefully, don't fire yet
        └─ Unknown      → touch, vibration, echolocation or a custom sense

Get Sense Contributions (Target) gives each sense's share when you need finer detail.

React to being shot from nowhere#

On AI Damaged (Instigator, Amount, Damage Type Tag, Hit Location)
  ├─► play a flinch montage
  ├─► Blackboard InvestigateLocation = Get Last Known Position (Instigator)
  └─► Report Pain from Definition (DA_Pain_Bleeding, Amount / 200)

With Damage Sense the shooter is already believed in, placed where they stood. For hardcore stealth turn Auto Confidence from Damage off, so a silenced hit hurts without revealing the shooter. Emotions & pain

Squads#

One sees you, the others come#

Each AI at Begin Play: Set Squad ID (Patrol_A). Auto Share on Detect is on by default, within Squad Share Range (3000). Squads & teams

Converge without telepathy#

Profile: Auto Share on Detect and Auto Share on Track both off.
Share after a visible call-out: On AI Detect → play a "Contact!" montage → on its notify, Share Target with Squad (Target).
On the receiver, branch on Stimulus = Shared Intel and approach carefully.

Without step 3, one guard spots you and four others shoot you through a wall.

Split up combat roles#

Request Combat Role (Flanker), else (Suppressor), else Approacher; Release Combat Role on On AI Forget. Four guards give one flanker, one suppressor and two approachers, no manager. Squads & teams

Bigger changes#

A Pain Type DA_Pain_Flashbang (Decay Rate 0.5, Amount Override 1; Sense Effects Vision Sense 1, Hearing Sense 0.5), and when the grenade goes off, Report Pain from Definition on each guard with a clear line to it. Emotions & pain

Switch to an alert profile#

Alarm raised
  └─► for each guard: Set Profile (DA_Profile_Guard_Alerted)

Make the alert profile a child of the base one so the swap keeps everything the AI believes. Profiles

A disguise#

Add Target Evidence (Player, "Disguise", Clamp (ceiling), 0.15) on each guard holds their belief at or below 0.15 even while they see you; Remove Target Evidence when the disguise is blown. Confidence The demo's Q4 does it with relationships instead: Squads & teams.

Tune one enemy without a new asset#

Begin Play
  ├─► APS Core → Set Profile Number (VisionMaxRange, 3200)
  └─► APS Core → Set Profile Flag (bEnablePeripheralCone, true)

Or fill in Profile Overrides on the APS Core. The change lands on a private copy: the asset and every other AI are untouched, and nothing it believes is reset. Use the override name shown on the profile reference. For every AI at once while playing: aps.Tune VisionMaxRange 3200 in the console.

Perceive something that isn't a Pawn#

Add an APS Target Component (it registers itself), or call Register Perceivable Actor at Begin Play and Unregister Perceivable Actor at End Play. How APS thinks

Add your own sense#

A Blueprint child of Sense Unit that answers Get Sense ID and Evaluate, added to Sense Classes. It fuses with the others and shows in the Visualizer. Custom senses