How can I achieve this "security camera" effect? I want to create the following effect:

When a keyboard control is pressed the main camera will be switched to another camera that already exists in the scene. At that time till the camera is switched back, everything at the scene where both cameras exist must remain as is with no change, except a few things of my choosing.

How can I achieve this? I thought of suspending the scene but I want to be able to move the new camera.

My 2nd thought was changing all objects to different states when I set the new camera so they won't move at all, but that will mess with scripts and it is confusing.

My 3rd thought was a bit more complicated but till a point I think correct. It was the following idea: What if I add the new camera in the original scene and create a new overlay scene with one new camera there also. Now everytime I switch to the new camera in the original scene, I'll suspend the original scene and add the overlay scene with a small delay so that it will seem that it is the same "new" camera. But there is a problem. How can I save any motion done with the camera in the overlay scene to be copied to the "new" camera in the original scene?

I hope I did not make this too complicated. Any ideas?
Switching a camera is pretty easy with the Scene Actuator in "Set Camera" mode.

Switching controls/behavior is independent from the camera, as it has no relation to what is rendered. Typically you "enable" a set of controls while you "disable" another set of controls.

There are many ways to achieve this effect. The basic idea is that each entity remembers if it is enabled or disabled (= state) and acts accordingly.

Additionally you need a way to request one or multiple state changes e.g. via property change, message listening or other events.

Example:
When receiving message "enable security camera", you 


let the camera switch to the security camera, 
disable the current controls on the player's avatar
enable the controls on the security camera
...


When receiving message "enable security camera", you 


let the camera switch to the player's camera, 
disable the controls on the security camera
enable the controls on the player's avatar
...


if you have a lot of such objects and possible toggles, you might want do this is two steps:


disable all
enable what was requested


This way you do not care the previous state.