Visitors are allowed in the PAU, but must be buzzed in and checked at the nursing station to ensure that they are not carrying anything harmful.
Many people experiencing a mental health emergency are very paranoid. It is important to respect their needs by not doing anything that aggravates their state.
I visited a friend in a PAU two years ago. I checked in at the nursing station, then went and sat down, confident that as a former patient I knew the ropes.
Turns out I was overconfident (maybe I was hypomanic? I can't remember). Anyhow, I pulled out my phone to check messages while waiting to be allowed to see my friend.
Almost right away a nurse was over, whispering to me "Put that away immediately, please. You may not understand, but many of our patients are paranoid, and that will aggravate them. They think you are taking pictures or recording them."
Having been one of those paranoid patients in the past, I was mortified at this basic error. I was overconfident, and reliving my own experience. I was not being a good guest.
It was humbling, and a good reminder that as a visitor I had an important role to play as a supporter, not as a former patient. Letting go of my past in hospitals was vital - and once I learned that lesson, I was able to listen much better to my friend and to hear his own experiences, without constantly looking at them through the lense of my own.