It's a film where as far as i can remember, 3 (possibly 4) random people awake in a room with one door which is locked. As far as I am aware they have no idea how they got into the room. I think they might be instructed to do some kind of survey, but soon realise they won't make it out alive. I think they might find scratches on the wall saying HELP or something similar... One of them gets shot by another one, and eventually I am fairly sure they all get gased and die.
Please help my memory with what the film was called?!
Thanks!