trigger_once
Spawnflags
| SF_TRIGGER_CHECKANGLES | 8 (borrowed from Quake; the trigger works only if its angles and the angles of the object are pointing in the same general direction on YAW) |
| SF_TRIGGER_ALLOWPHYSICS | 16 (tells the trigger to respond to all physical objects, not necessarily func_physbox) |
Option
| netname | Filter for activating only objects of a specific class (classname) or with a specific name (targetname). |