Q. The Aron Hakodesh in the shul I daven, has a proper paroches curtain. The doors behind them are made of artistic bars that permit seeing the sifrei torah inside the ark. Often they are locked with a chain and lock. If someone gets pesicha for selichos or avinu malkenu, does he have to unlock the doors? (You can see the sifrei Torah, and sometimes the key isn’t readily available).

A. The purpose of the Aron Hakodesh doors and the paroches curtain is debated by Poskim. Maharam Padova (82) and others maintain it serves the Aron Hakodesh, since it is appropriate to separate between the holy and the mundane.
Terumas Hadeshen (I: 68) opines that since it is used primarily with the door of the Aron Hakodesh closed, it does not touch the Sifrei Torah and also does not even directly separate between the sefarim and the congregation, it is only a utensil of the shul. Remah (O.H. 154: 6) rules accordingly that the paroches we place in front of the Aron Hakodesh, has only the holiness of a utensil of the beis haknessess and is not considered a direct service vessel or tashmish to the Torah.
The above may make a difference in our case regarding whether one may hang the paroches before the Aron Hakodesh on Shabbos. We rule (See Shulchan Aruch, O. H. 315: 1), that it is forbidden to erect a vertical partition only when it serves a defined, Halachic function (as the wall of a sukka). According to the Terumas Hadeshen the paroches lacks a defined, halachic function but just serves for added tzenius or modesty.
Horav Shlomo Miller’s Shlit’a opinion is that it may be considered pesicha, when you can actually see the Sifrei Torah through the bars of the doors after you open the paroches, in case of need and tircha detziburo to fetch the keys.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a