Object position

Place this code inside your object's script, or create a new one and add this code to it:

 void Update () {
     if (Camera.main.WorldToViewportPoint (transform.position).x > 0.5f) { // checks if it's on the right side. 
         // it's on the right side
         Debug.Log ("right side of screen");
     } else { // if not, then it must be on the left side
         // it's on the left side
         Debug.Log ("left side of screen");
     }
     // add all of the code to the Update() function
 }

This is untested. Let me know if you have any problems.