dont get dont knock twice! its a baaad game (get layers of fear or Outlast instead!) . heard perception isnt so good either. a shame...was interested in it too.
Do not waste your money on dont knock twice, there is a shit ton of bad reviews and gameplay wise it isnt worth it.
Perception is a neat idea but your better of waiting for it to be cheaper since the whole blind concept is ruined by the sensor thing.