Robot.cs

using UnityEngine;
using System.Collections;
using UnityEngine.AI;

public class Robot : MonoBehaviour
{
    public float rayLength = 20f;
    GameObject target;
    float startRotation;
    float t = 0;
    public float maxTurnAngle = 45.0f;
    GameObject valonlahde;
    public AudioClip alert;
    GameObject player;

    // Use this for initialization

    void Start()
    {
        startRotation = transform.rotation.eulerAngles.y;
        valonlahde = GameObject.Find("Hehku");
        player = GameObject.FindWithTag("Player");
    }

    // Update is called once per frame
    void Update()
    {
        if (target == null)
        {
            Turn();
            DetectPlayer();
        }
        else
        {
            Move();
        }
    }

    void Move()
    {
        NavMeshAgent agent = GetComponent<NavMeshAgent>();
        agent.SetDestination(target.transform.position);
    }

    void DetectPlayer()
    {
        Debug.DrawRay(transform.position, transform.forward * rayLength, Color.red);
        RaycastHit hitInfo;
        if (Physics.Raycast(transform.position, transform.forward, out hitInfo, rayLength, 1))
        {
            GameObject hitGameObject = hitInfo.collider.gameObject;
            if (hitGameObject.tag == "Player")
            {
                target = hitGameObject;
                valonlahde.GetComponent<Light>().color = Color.red;
                AudioSource.PlayClipAtPoint(alert, player.transform.position);
            }
        }
    }

    void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.tag == "Player")
        {
            GameObject.Find("Level").SendMessage("Kill");
        }
    }

    void Turn()
    {
        t += Time.deltaTime;
        transform.rotation = Quaternion.Euler(0, startRotation + Mathf.Sin(t) * maxTurnAngle, 0);
    }

}