You can read more about application events at Chip Pearson's site:
http://www.cpearson.com/excel/AppEvent.aspx

FYI: these events fire when you stay within Excel. If you swap applications,
they don't fire.

Kent Prokopy wrote:

I need a way to have a sub within my xla to run every time any workbook gets
or losses focus. So if a new workbook is opened or closed, or you just switch
back and forth between two workbooks.

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Dave Peterson