Event.alt

Is Alt/Option key held down? (Read Only)

On Windows, this returns true if any Alt key is held down.
On Mac, this returns true if any Option key is held down.

JavaScripts

// Prints Option or Alt key was pressed depending the
// platform this script is being run.
function OnGUI() {
var e : Event = Event.current;
if (e.alt) {
if(Application.platform == RuntimePlatform.OSXEditor) {
Debug.Log("Option key was pressed");
} else if( Application.platform == RuntimePlatform.WindowsEditor) {
Debug.Log("Alt Key was pressed!");
}
}
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void OnGUI() {
Event e = Event.current;
if (e.alt)
if (Application.platform == RuntimePlatform.OSXEditor)
Debug.Log("Option key was pressed");
else
if (Application.platform == RuntimePlatform.WindowsEditor)
Debug.Log("Alt Key was pressed!");

}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def OnGUI():
e as Event = Event.current
if e.alt:
if Application.platform == RuntimePlatform.OSXEditor:
Debug.Log('Option key was pressed')
elif Application.platform == RuntimePlatform.WindowsEditor:
Debug.Log('Alt Key was pressed!')