Weeping angle ai help

im trying to make a weeping angle ai(a ai that only moves if the player arnt looking at it)

but the problem is that i dont how make it make only move if the camera field of view arnt on it. Im thinking too make a field off view float on the player that match the camera field of view and as long as ai is in this field of view it got a bool that is false and cant move or if there is better way to do it (im pretty new to unity too)

this is my update() code and my chase() code that only show how it's actions and it's movement right now, im using navmestagent on my ai too

 void Update () 
     {
       playerDistance = Vector3.Distance(Instance.TheInstance.ThePlayer.transform.position, transform.position);
 
         if (playerDistance < 3f)
         {
             attack();
         }
         if (playerDistance < 15f)
         {
            lookAtPlayer();
             
         }
         if (playerDistance < 2f)
         {
             nav.Stop();
         }
         if (playerDistance < 12f)
         {
             if (playerDistance > 2f)
             {
                 chase();
             }
            
         }
           
   }
  
 void chase()
     {
         nav.SetDestination(Instance.TheInstance.ThePlayer.transform.position);
     }