void OnTriggerEnter (Collider other)
     {
         if (other.gameObject.tag == "Object") 
         {
             Debug.Log ("Collided");
         }
  
//at least one object needs a rigidbody, and a collider set to isTrigger.
//the problem may be that you put it in a void, you need to take it out of voids for it to work