GUIUtility.hotControl

static var hotControl : int

Description

The controlID of the current hot control.

The hot control is one that is temporarily active. When the user mousedown's on a button, it becomes hot.
No other controls are allowed to respond to mouse events while some other control is hot.
once the user mouseup's, the control sets hotControl to 0 in order to indicate that other controls can now respond to user input.

JavaScripts

// Click on the button to see the id

function OnGUI() {
GUILayout.Button("Press Me!");
Debug.Log("id: " + GUIUtility.hotControl);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void OnGUI() {
GUILayout.Button("Press Me!");
Debug.Log("id: " + GUIUtility.hotControl);
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def OnGUI():
GUILayout.Button('Press Me!')
Debug.Log(('id: ' + GUIUtility.hotControl))