alarm on a date cell
 

I have a series of cells that I would like to trigger a pop up alarm to show
a due date in that cell, I,m currently using an adjacent cell with the
function =IF(A1<=TODAY(),"OVERDUE","") then conditional formatting to turn
the cell red, as the workbook contains many sheets all of which I would have
to scan to observe any alarms I would love to have a pop up alarm when I
opened the workbook, thanks for your help.