Directors megaphone is a useful instrument for him. Actually the director's job is a very hectic and stressful work. He has to keep a lot of thing to his memory like which actions will be taken by whom or so.
At some point of time he needs to gather the whole team and start the shoot. That is where Directors megaphone comes in to consideration to make a wake up call to the actors and the working unit. He can also use it during the shoot to make the actors hear properly what he wants to say and to the responsible unit as well.
