如何确定Windows Mobile中的程序中断

I have an game application I have written for Windows Mobile and I want to have a timer associated with the puzzle. If the program loses focus for any reason (call comes in, user switches programs, user hits the Windows button) then I want a pop up dialog box to cover the puzzle and the timer to stop. When the user closes the pop up dialog the timer can start up again.I have an game application I have written for W