Why doesn't OnParticleTrigger fire?

Particle System Triggers module needs colliders explicitly listed. Drag the trigger collider into the Colliders list. Set Inside or Outside action to Callback. OnParticleTrigger fires per frame with affected particles.

How do I read which particles are inside?

In OnParticleTrigger, call ps.GetTriggerParticles(ParticleSystemTriggerEventType.Inside, ref insideParticles). Modify the list and re-set; particles can be killed or have properties changed.

Trigger detection runs per particle per collider. Small colliders + few particles = negligible. Large lists or huge particle counts add CPU. Use bounds-trimmed colliders.

Fix: Unity Particle System Trigger Collider Not Detecting

Quick answer: Triggers module → drag colliders into the Colliders list. Set Inside / Outside / Enter / Exit to Callback. Implement OnParticleTrigger; call ps.GetTriggerParticles to read affected particles.

You want particles destroyed when entering a damage zone. Triggers module enabled. OnParticleTrigger never fires.

The Symptom

OnParticleTrigger callback not invoked despite particles overlapping a collider. Colliders module is on; visual collisions work for bounce/kill but not the trigger event.

The Fix

Particle System → Triggers module:
  Inside:    Callback
  Outside:   Ignore
  Colliders:
    [0] DamageZoneCollider

Each collider must be explicitly listed. Set the action to Callback for the events you care about.

void OnParticleTrigger()
{
    var ps = GetComponent<ParticleSystem>();
    List<ParticleSystem.Particle> inside = new();
    int count = ps.GetTriggerParticles(ParticleSystemTriggerEventType.Inside, inside);
    for (int i = 0; i < count; i++)
    {
        var p = inside[i];
        p.remainingLifetime = 0;   // kill
        inside[i] = p;
    }
    ps.SetTriggerParticles(ParticleSystemTriggerEventType.Inside, inside);
}

Verifying

Spawn particles into the trigger zone. They should disappear instantly. Print on entry to confirm OnParticleTrigger fires.

“Colliders listed. Action Callback. GetTriggerParticles works.”

Related Issues

For sub-emitter inheritance, see sub-emitter. For burst not firing, see burst.

List the colliders. Read the particles.