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Ai sound.png

ai_sound is a point entity available in all Source games. This entity makes abstract sounds or smells that can be sensed by NPCs, but not by the player. This can be used to cause reactions in nearby NPCs. An entity called soundent appears to help with managing AI sounds when the game runs.

In code, it is represented by class CAISound, defined in soundent.cpp.


Volume (volume) <integer>
How far away this sound can be heard. This is a radius.
Duration (duration) <float>
How long the sound persists each time it plays.
Sound Type (soundtype) <choices>
The type of sound or smell will determine the reaction of NPCs that sense it. Some of these are not in the FGD, so their associated number must be typed manually.
Literal Value Description
1 Combat: Will cause most NPCs to become alert
2 World: Will cause most NPCs to become alert
4 Player: Feign player audible
8 Danger: Will cause most NPCs to move away from the position of the sound
16 Bullet Impact
32 Carcass
64 Meat
128 Garbage
256 Thumper: causes antlions to run away briefly
512 !FGD Bugbait: get nearby antlions' attention
1024 !FGD Physics Danger: Scares off npc_metropolice, npc_combine_s, and npc_antlion
2048 !FGD Sniper Danger: Scares npc_snipers into their hole
4096 Move Away: Pushes away npc_metropolice, npc_citizen, npc_combine_s, npc_alyx, npc_barney, npc_fisherman
8192 !FGD Player Vehicle: Makes NPCs hear the player & makes npc_metropolice turn towards the sound (only used by prop_vehicle_airboat
16384 Player Companion Readiness: Low
32768 Player Companion Readiness: Medium
65536 Player Companion Readiness: High
Additional sound context (optional) (soundcontext) <choices>
Optional settings specifying such things as who can or cannot hear the sound. Many of these are not in the FGD and some of them have not been fully tested.
Literal Value Description
1048576 !FGD Sound is from Sniper
2097152 !FGD Gunfire (use with combat sound type)
4194304 !FGD Mortar (pending explosion)
8388608 Only Combine hear/smell
16777216 !FGD React to source (faces the ai_sound instead of location proxy)
33554432 !FGD Explosion (use with combat sound type)
67108864 Exclude Combine (Combine don't hear/smell)
134217728 !FGD Danger approach (react with danger if you see the ai_sound, just face if otherwise, shouldn't work with location proxy)
268435456 !FGD Only allies (npc_citizen, etc.) hear/smell
Location Proxy (locationproxy) <targetname>
If you specify an entity here, the sound will be made at that entity's location (!player is an option).


Classname (classname) <string>
The classname defines the type of entity. Classnames can be changed using AddOutput, which will influence how the engine deals with the entity in certain circumstances.
Name (targetname) <string>
The name that other entities refer to this entity by.
Global Entity Name (globalname) <string>
Name by which this entity is linked to another entity in a different map. When the player transitions to a new map, entities in the new map with globalnames matching entities in the previous map will have the previous map's state copied over their state.
Parent (parentname) <targetname>
Specifies a movement parent. An entity will maintain its initial offset from its parent. An attachment point can be added to the end of the name, separated by a comma. Every entity can be parented, even point entities. Entities which are parented will be forced to transition to the next map, such as from a trigger_transition. Some entities which aren't intended to be parented may not function correctly. phys_constraint can be used as a workaround to parenting.
Origin (X Y Z) (origin) <coordinates>
The position of this entity's center in the world. Rotating entities typically rotate around their origin.
Pitch Yaw Roll (X Y Z) (angles) <angle>
This entity's orientation in the world. Pitch is rotation around the Y axis, yaw is the rotation around the Z axis, roll is the rotation around the X axis.
Note.png Note: This works on brush entities, although Hammer doesn't show the new angles.
Flags (spawnflags) <integer>
Toggles features of an entity, its specific number is determined by the combination of flags added.
Response Contexts (ResponseContext) <string>
Pre-defined response system contexts for this entity. Format is key:value,key:value,.... Contexts may be filtered.
Effects (effects) <integer> !FGD
Combination of effect flags to use.
Local Time (ltime) <float> !FGD
The local time of the entity, independent of the global clock. Used mainly for physics calculations.
Next Think (nextthink) <float> !FGD
Amount of time before the entity thinks again.
Hammer ID (hammerid) <integer> !FGD
The entity's Hammer ID. Mainly used by plugins and debugging commands, such as ent_keyvalue. Can be manually assigned with the "hammerid" or "id" keyvalue. Entities spawned at run-time are not assigned any Hammer ID.


InsertSound <integer> <Obsolete>
Deprecated. Insert a sound in the AI sound list at a specified volume (1-100) which influences detection radius.
Make the Sound.


Removes this entity and any entities parented to it from the world.
Functions the same as Kill, although this entity and any entities parented to it are killed on the same frame, being marginally faster than Kill.
SetParent <string>
Move with this entity. See Entity Hierarchy (parenting).
SetParentAttachment <string>
Change this entity to attach to a specific attachment point on its parent. The entity will teleport so that the position of its root bone matches that of the attachment. Entities must be parented before being sent this input.
SetParentAttachmentMaintainOffset <string>
As above, but without teleporting. The entity retains its position relative to the attachment at the time of the input being received.
Removes this entity from the the movement hierarchy, leaving it free to move independently.
AddOutput <string>
Evaluates a keyvalue/output on this entity.
Format: <key> <value>
Format: <output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
FireUser1 to FireUser4
Fire the OnUser outputs; see User Inputs and Outputs.
Use  !FGD
Same as a player invoking +use; may not do anything. Can also be invoked by creating an output that does not specify an input.
This input is not included in Valve's FGDs.
DispatchEffect <string> (removed in <Left 4 Dead>) !FGD
Dispatches a special effect from the entity's origin. Removed and replaced entirely by the particle system since <Left 4 Dead>.
DispatchResponse <string> !FGD
Dispatches a response to the entity. See Response and Concept.
AddContext <string>
Adds to the entity's list of response contexts. Format is <key>:<value>.
RemoveContext <string>
Remove a context from this entity's list. The name should match the key of an existing context.
ClearContext <string>
Removes all contexts from this entity's list.



OnUser1 to OnUser4
These outputs each fire in response to the firing of the like-numbered FireUser1 to FireUser4 Input; see User Inputs and Outputs.