To be able to trap application events across all open workbooks in MS Excel via an add-in follow these steps.

1. Add a class module
   In the class module enter the following at the top of the module
   Public WithEvents xlApp as Application Then you will be able to write code within any of the application events.
2. Add a global variable in a standard module of the class type created in 1.
3. In your initialisation code for the Add-in, call a routine to initialize the class application object
   eg.

   Sub TrapApplicationEvents()
      set globalvar = new classApp
      set globalvar.xlApp = Application
   End Sub