Locked is usually danger to self or others or very severe cases. Unlocked - milder cases, patients undergoing inpatient ECT, etc. Usually it is 2 people per room.

At the teaching hospital the unlocked unit also had a stationary bike you could use, and an enclosed garden which was nice. The locked unit patients could not go to the garden by themselves - some of them who had special privileges went under the supervision of staff.

If you are suicidal and are receiving an IV, as I was, you are not allowed, on a locked unit, to be in your room. You have to stay in the hallway.