Chapter 8:
There are 3 bed rooms in the bed carriage. The first will unlock and give you a keycard and a note early in this chapter. The second room unlocks after you find the button to the secret carriage and also has a note and the third room unlocks when you run away out of the secret carriage. I did read them one by one, but it might be possible to just read them all after unlocking the last 2.