From Valve Developer Community
- Fires when an NPC picks up this weapon. (activator is the NPC)
- Fires when the player +uses this weapon. (activator is the player)
- Fires when a player picks up this weapon. (activator is the player)
- Fires when the player 'proves' they've found this weapon. Fires on: Player Touch, +USE pickup, Physcannon pickup, Physcannon punt.
- These outputs each fire in response to the firing of the like-numbered
FireUser4Input; see User Inputs and Outputs.