Locker;¬Screen Locker Switch
The following buttons allow you to enable screen locking and screen saving:

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Locker;¬Screen Locker Switch
BackSpace can be set to lock your screen when the screen saver kicks in.  Implicit in this is that the screen won't lock unless you have a screen locking password, enable the screen lock feature, and either have the screen saver enabled or manually initiate the screen saver.  This screen locker shouldn't be thought to provide extensive security, but it will keep most casual interlopers out.  You should NOT use you account password as your screen locking password, because a bad person could rather easily monitor the passwords given to BackSpace.  Nevertheless, both the user's account password and the root password can be used to unlock the screen.

You can still turn the power off even if the screen is locked.  When the Power key is pressed, the Workspace application will activate and display a panel asking you to confirm the power-off request, though you won't see this panel because it will be behind the screen saver's display.  If you then type return, the computer will turn off.  However, you can still unlock the screen after the user has pressed the Power button.  You must move the mouse to bring up the password panel.  You must then click in the panel to activate BackSpace (so it accepts keystrokes) and type your password but do NOT press return.  After a short period, BackSpace will accept your password and unlock the screen.  You can then cancel the power-off request.
 
You should be considerate with the use of the screen locker.  BackSpace should not be used to lock the screen for an extended period of time on a machine intended for public use; this usage could deprive others who really need to use the public machine.  

Saver;¬Screen Saver Switch
If you select the screen saver feature, BackSpace will act as a screen saver; When the computer has been inactive, you will be greeted by the selected screen saver rather than the normal dim screen.  You can also force the screen saver/locker into action by selecting "Do Screen Saver" from the menu or the Settings window.

BackSpace uses the timeout interval set via the Preferences application; however, it might not detect changes to the interval enacted after BackSpace is launched.

SaverButton;¬The "Do Screen Saver" Button
Clicking this button immediate activates BackSpace's screen saver, and the screen locker if it is enabled.  This feature can also be activated from the menu or with its key equivalent:
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or by moving the cursor to a preselected "hot corner".

HotCorner;¬Hot Corners
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This icon allows you to select a hot corner.  If you move the mouse to the selected hot corner, the screen saver will activate after a few seconds.  You can disable this feature by clicking the indicated corner so that it is not checked.