Why doesn't OnCollisionEnter fire when two static colliders touch?

Static-vs-static contacts produce no events — PhysX skips them by design. At least one body in the pair must have a Rigidbody (kinematic counts) for collision callbacks to dispatch.

Trigger events fire when one collider is a trigger AND at least one has a Rigidbody. Add a Kinematic Rigidbody to the moving piece; OnTriggerEnter then fires reliably.

Can I use a Kinematic Rigidbody to make a moving platform?

Yes. Set Rigidbody.isKinematic = true. Move via rigidbody.MovePosition for proper interpolation. Other static bodies it touches now emit collision events.

Fix: Unity OnCollisionEnter Not Firing Between Static Colliders

Quick answer: Add a Rigidbody (Kinematic if you don’t want gravity) to at least one collider in the pair. Static-vs-static doesn’t emit events. Trigger pairs also need a Rigidbody.

Two pre-placed colliders touch — OnCollisionEnter never fires. PhysX considers them both static and skips event dispatch.

The Symptom

Collision script attached, both objects have colliders, they visibly overlap, no callback. Adding a Rigidbody fixes it.

The Fix

// Wall (no Rigidbody)
- BoxCollider

// Door (needs callback)
- BoxCollider
- Rigidbody (isKinematic = true, useGravity = false)

Door now counts as Kinematic Rigidbody for physics. Touching the wall fires OnCollisionEnter on door’s scripts.

Trigger Variant

// Pickup zone
- BoxCollider (isTrigger = true)
- Rigidbody (isKinematic = true)

// Player
- CharacterController OR Rigidbody + Collider

Trigger needs a Rigidbody on at least one side. CharacterController internally uses physics so it counts as the moving party.

Verifying

Print on OnCollisionEnter / OnTriggerEnter. With Rigidbody added: fires. Without: silent.

“Rigidbody on one side. Kinematic if no gravity. Callbacks fire.”

Related Issues

For OnTriggerExit on disable, see trigger exit. For Rigidbody sleep, see sleep waking.

Add a body. Events fire.