Who Are You?(2010)

Original title: ใคร...ในห้อง

Nida is a single mother who takes care of her anti-social son who has locked himself in his room for five years. The only way to communicate with her son is to write on a piece of paper and slip it under the door. But, when outsiders start to get curious about what is going on behind the door of her son's room, a series of terrible events starts to happen.