This is a modified tutorial from Dromed Central. Author: Unknown.

This tutorial explains how to set up traps that shoot broadheads, magic missiles, etc.

You’ll need 2 things:
1. EmitterTrap or EmitStreamTrap
2. A switch of some sort.

Go into the Object Hierarchy:
fnord>TrigTrap

There are two objects of interest here:
EmitterTrap (-2555)
EmitStreamTrap (-2541)

The difference between the two is that EmitterTrap only shoots once. Place the EmitterTrap in the location that you want. By default it aims south. That’s down when looking at the monitor. Open its Properties, and click Add>Tweq>Emit. This will bring up a new window. This is what the trap will shoot, how fast, and in what direction.

Halt - Leave as Stop Tweq
AnimC - Leave as Sim. NoLimit, Sim for EmitStreamTrap
MiscC - Leave as Grav
CurveC - Leave as None
Rate - 1. 1000 for EmitStreamTrap
Max Frames - 1. 0 for EmitStreamTrap
Emit What - broadhead
Now this is what you’ll change to decide what it is shooting. Here is a list of things I have found that works:

broadhead
rock
webshot
Tiltawhirl
apple
sword
magicmissle

But the list could be just about any object. Play around with it and see what you can do.

Velocity - X = 0, Y = 0, Z = 0. This is the speed of the object that is fired. Also the direction X is north and south. North will be a negative number and south a positive number. Y is east and west. East will be a positive number and west will be a negative number. Z is up and down. Up will be a positive number and down will be a negative number.

Create a control-device for the trap. This can be any of the following: Room Brush, Object, or Trap. Rooms can be used with a TrigRoomPlayer script added to the roombrush. Object can be a PressurePlate or other objects with a StdButton script added to it. Trap is a BoundsTrap. When you’ve decided on a trigger, just link it to the EmitterTrap with a ControlDevice link.

Example: Create a switch(physical>Gizmo>Switches>Levers>Up/Down Switch). Click its Links and then Add.
Choose ControlDevice in the Flavor field.
From: the number of the Up/Down Switch.
To: the number of the EmitterTrap.

When using the switch, the trap should now go off.