This selects the space in which to simulate particles. It can be either world or local space.

var useLocal : boolean = true;

function Start () {
	useLocal = (particleSystem.simulationSpace == ParticleSystemSimulationSpace.Local);
}

function Update () {
	particleSystem.simulationSpace = (useLocal ? ParticleSystemSimulationSpace.Local : ParticleSystemSimulationSpace.World);
}

function OnGUI() {
	useLocal = GUI.Toggle(new Rect(10, 60, 200, 30), useLocal, " Use Local Simulation Space");
}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    public bool useLocal = true;
    void Start() {
        useLocal = particleSystem.simulationSpace == ParticleSystemSimulationSpace.Local;
    }
    void Update() {
        particleSystem.simulationSpace = ((useLocal) ? ParticleSystemSimulationSpace.Local : ParticleSystemSimulationSpace.World);
    }
    void OnGUI() {
        useLocal = GUI.Toggle(new Rect(10, 60, 200, 30), useLocal, " Use Local Simulation Space");
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	public useLocal as bool = true

	def Start() as void:
		useLocal = (particleSystem.simulationSpace == ParticleSystemSimulationSpace.Local)

	def Update() as void:
		particleSystem.simulationSpace = (ParticleSystemSimulationSpace.Local if useLocal else ParticleSystemSimulationSpace.World)

	def OnGUI() as void:
		useLocal = GUI.Toggle(Rect(10, 60, 200, 30), useLocal, ' Use Local Simulation Space')