AudioListener.volume

static var volume : float

Description

Controls the game sound volume (0.0 to 1.0)

JavaScript
AudioListener.volume = 0.5;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Example() {
AudioListener.volume = 0.5F;
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Example():
AudioListener.volume = 0.5F