If camera has rendered

Hi,
I’m trying to get unity to print something in the console if a prefab in the screen comes in to view, but only if it’s in view.
I’m trying to do something like this

public GameObject theObject;


if (theObject.isVisible) {
    isVisible = true;
}

if (!isVisible) {
    if (!right && !up) {
                Debug.Log ("Not visibile");
            }
        }

I’ve looked at these threads but they haven’t helped;

http://answers.unity3d.com/questions/8003/how-can-i-know-if-a-gameobject-is-seen-by-a-partic.html?page=1&pageSize=5&sort=votes

isVisible is a property of the Renderer component not of gameobject…