A collision trigger (or trigger volume) is a shape in Unreal Engine that detects when actors enter or leave it, without physically blocking them. It generates overlap events but has no collision response — things pass right through.
How It Works
You create a shape component (UBoxComponent, USphereComponent, or UCapsuleComponent) and set its collision profile to Trigger:
BoxComponent->SetCollisionProfileName(TEXT("Trigger"));Then bind to its overlap events:
BoxComponent->OnComponentBeginOverlap.AddDynamic(this, &MyClass::OnBeginOverlap);
BoxComponent->OnComponentEndOverlap.AddDynamic(this, &MyClass::OnEndOverlap);The physics engine handles detection. When another actor’s collision shape overlaps the trigger, OnBeginOverlap fires. When it leaves, OnEndOverlap fires. No per-frame cost for the detection itself — it’s all event-driven.
Common Uses
- Interaction zones — the NGInteractionSystem uses a box trigger around the player to detect nearby interactable objects
- Kill volumes — trigger at the bottom of the map that destroys anything that falls off
- Area transitions — entering a trigger loads the next level or activates a cutscene
- Sound zones — changing ambient audio when the player enters an area
Trigger vs. Collision
The key difference is response:
- Trigger (
Overlap) — generates events, no physical blocking. Actors pass through. - Collision (
Block) — generates events AND prevents movement. Actors stop or bounce off.
Both use the same underlying physics system. The difference is just the collision response setting.