Previously, I was using Stop action particles, in a manor somewhat similar to touch triggers, to detect when a particle hit something and play a sound
An example would be the sound of a missile exploding on impact (Done by an invisible trigger particle shot along side the visual particle)
The setup is similar to how particle based touch triggers work, except it's triggered by contact with the world (and thus, a purely touch trigger system would not be suitable)
I believe a similar system is used in avatars that have an effect when you swing a sword fast enough.