Ray cast from object to detecting hit, draws a red line when a hit is detected otherwise draws a green light forward from object.

Unity Raycast block on Update()

void Update () {

	RaycastHit hit;
  	Vector3 fwd = transform.TransformDirection(Vector3.forward);
	
  	if (Physics.Raycast(transform.position, fwd, out hit, 10.0F)){
    	print("There is something in front of the object!");
    	Debug.DrawLine(transform.position, hit.collider.gameObject.transform.position, Color.red);
  	}
		
  	fwd =  transform.TransformPoint(Vector3.forward * 4);
  	Debug.DrawLine(transform.position, fwd, Color.green);
}