How to use particle systems to check if an object is moving fast:

No Udon required, works in the current trigger system. Might already been done by one of the vrchat grand wizards but I haven't seen it so here it is. This will test to see if an object's velocity is above a certain threshold. It's just a simple boolean test, it won't tell you how fast the object is moving, just that it's moving faster than a certain speed you have chosen.

1. Create two new layers: Speed Particle and Speed Test. Check the physics matrix in your project settings and make it so these layers only collide with each other.
2. Stick a particle system on the object you want to speed test and put it on the Speed Particle layer.
3. Make sure the particle system is looping, with a duration as long as the particle's lifespan, simulated in worldspace and with transform as the emitter's velocity.
4. Add a burst at the start of the emitter's loop.
5. Add the inherit velocity subcomponent, with mode current, so it gets continuous velocity of the system
6. Add size-by-speed subcomponent. Adjust the curve so it's flat until the very end of the range. Adjust the maximum value of the speed range, the test speed goal is just below this value.
7. Add a collision subcomponent. Set it to collide with world, high quality, no bounce, 1 lifetime loss, send collision messages and only let it collide with the Speed Test layer.
8. Add a new object alongside the particle emitter with a collider and set this object to the Speed Test layer. Adjust the size of the collider on this object so it only hits the particle's collider when it is large (easy to see in the editor)
9. Add a trigger to that new object of type OnParticleCollision and have it do whatever actions you want (like open the door or activate the damage effect or whatever)