UEFN Scene Graph Hearing Detection: React to Sounds and One-Shot Pulses

UEFN Scene Graph hearing detection pairs a hearing emitter with a detector so an entity can react to a sound signal. Fortnite 43.10 introduces it as part of experimental Perception. You can test an alarm or a creature reacting to footsteps, but an island using these APIs cannot be published yet.

A sound file playing in your level does not automatically reach a hearing detector. The source needs a hearing_emitter_component, the listener needs a hearing_detector_component, and your Verse logic must subscribe to the events. Only then can you trigger a reaction.

How UEFN Scene Graph hearing detection works

Use a hearing_emitter_component on the entity producing the hearing signal and a hearing_detector_component on the observer. Hearing information can be continuous once passive emission is explicitly enabled, or sent as a one-shot pulse. The sense event can carry loudness, position and gameplay tags.

Subscribe a receiver to the detector, with a filter that passes relevant sounds, before expecting events to arrive.

UEFN Scene Graph hearing detection: continuous sounds and pulses

A continuously detectable emitter is a natural fit for something like a running generator or an active alarm. A pulse better represents a single event such as a dropped object or a door slamming. Treat them differently in your game logic.

A pulse should not leave a guard permanently acting as though a sound is still occurring. A continuous emitter should have a clear end condition. The common Perception event lifecycle provides detection states, while one-shot events can be reported as Instant.

Why listening volumes matter for UEFN Scene Graph hearing detection

Hearing is a spatial sense. Epic’s Perception documentation explains that spatial emitters and detectors can use a point or a mesh-defined volume. Detection happens when the relevant point lies inside the other side’s volume. Do not assume a louder number magically lets a listener hear through every boundary.

Test a listener inside the intended range, move it beyond the boundary and confirm your filter threshold is not excluding all of the events.

UEFN Scene Graph hearing detection: a simple stealth test worth building

To test UEFN Scene Graph hearing detection, use one observer, one emitter and a single clearly labelled sound category. Start with an obvious alarm pulse and log when the observer receives it. Only then try two different types, such as a low-priority footstep and a loud alert, with gameplay tags or loudness-based filtering.

This makes it much easier to tell a broken subscription from a game-design choice that intentionally ignores quiet noise.

Why an emitter may not trigger the detector

A common UEFN Scene Graph hearing detection problem is having no listening volume. Epic’s example uses a mesh_component on the listening entity to define the detection area. The source still needs its hearing_emitter_component. PassiveEmissionEnabled is false by default, so enable it explicitly for a continuously detectable source.

For a single footstep or alarm, call Emit with hearing_data to send a one-shot pulse instead.

Check which hearing events reach your listener

Test the hearing detector with an obvious one-shot alarm first. Log the event before tying it to a guard animation or movement. Then try a quieter pulse and a different gameplay tag so you can tell whether your subscription filter is doing what you intended. If both signals arrive, adjust the filter one condition at a time.

Move the emitter outside the listening volume and test again. Epic’s Perception documentation explains that hearing uses spatial points and volumes, so placement matters. If an event still arrives when it should not, inspect the detector’s mesh-defined area and the emitter’s position. Keep the sound players hear separate from the signals your gameplay logic processes.

UEFN Scene Graph hearing detection FAQ

Will an NPC automatically investigate the sound? No. You need to write the behaviour that handles a hearing event.

Can a detector react to a single footstep? Yes, if the emitter sends a pulse and the listener’s subscription accepts it.

Why are no events arriving? Check the emitter, listening volume and filter first.

Can this be published? Not while the Perception API is experimental.

Official source: Epic Games documentation.