I have seen Psych ERs and CPEPs -- both are different than just the medical ER experience.
When I say Psych ER, I mean a separate area, locked, yes, with all the support staff, glass wall, etc. Some have a few rooms and otherwise a big open space, I saw one with 10+ rooms and a smaller open space. The main decision is admit or discharge, and you won't really keep someone for over 24 hours (maybe you could, but it's just uncommon, I don't know).
For CPEPs, they are also separate, but you can basically admit for observation for 72 hours -- right there in the CPEP. It's the ideal thing for many of the patients, and for learning.
Then there are just those "psych ERs" that are cordoned off by tape or a hallway from the medical ER. I put it in quotes because it is not locked down... I saw one on the interview trail that had a kind of room/area to work, but otherwise looked like a medical ER -- and they frequently kept patients for over 24 hours.
Great to see first encounters, to be the one guessing about the dx, you can learn a lot. And if you like shift work.....