Can't Check if there are no Collisions

Hey, I am really new to Unity and I am trying to make an app.
All is going well except I need to check if there are any objects colliding with an object I have just floating. The aim of the game is to knock all the blocks off of the place. I have an invisible object with a box collider around all of the blocks. I want the collider to check 'if there are no blocks left on the plane, go to the next scene'. I am still trying to figure out how to do it.
This is what I have so far: (I am pretty new to this so I'm probably way off)

Spoiler: Code

Code (CSharp):

1. void OnCollisionStay(Collision other){
2.         if (other.rigidbody){
3.             Debug.Log ("On Plane");
4.         }
5.         else
6.         {
7.             Debug.Log ("Off Plane");
8.         }
9.     }

If anyone knows how to do it, please let me know.
(I know how to go to the next scene, I just don't know how to check if there is anything colliding with it)

 

If you know that you are going to have objects colliding with the plane for the duration of the game, except when they are all knocked off at the end, you could keep track of the number of collisions via a counter :

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using System.Collections.Generic;
4. public class CheckCollisions : MonoBehaviour {
5.  
6.     int collisionCounter = 0;
7.     // Use this for initialization
8.     void Start () {
9.        
10.     }
11.  
12.     void OnCollisionEnter(Collision other)
13.     {
14.         collisionCounter++;
15.     }
16.  
17.     void OnCollisionExit(Collision other)
18.     {
19.         collisionCounter--;
20.     }
21. }

Everytime a collision occurs, the counter goes up. When a collisions ends (knocked off the plane), then the counter goes down. Once the counter reaches 0, you know that youve finished the level.

 

@nostalgicbear Wow I was way off... This worked, thanks!