You can deploy them in your cockpit. They can be moved out at anytime. But Installation is basically "Deploying" the item. Once deployed you can Access the Control Panel and you'll be able to lock or unlock all your doors - that you've installed locks, simultaneously rather then doing it individually w/o a control panel.
I do not believe that it is password protected, though something along those lines would make for an interesting suggestion/addition to the game.
As for multiple control panels being deployed in a single entity and functioning, a coder would have to post here on how they are programmed, or better yet, give it a try when you get them. :)
Elijah, you are indeed correct you can have them deployed in any room.
As for your other question. You can HAVE multiple Panels deployed in multiple rooms. And they work as they can unlock in one and lock in another. I just tried it out.
However there is no password protection on the Security Control Panel. But that too would make for an interesting feature if one wanted to use it. Similar to opening a door.
You can't use SCP if you do not own it or its not assigned to you as commander. At least last time I tried it out =D So password is not really required unless they would let anybody use it who is in the room.