How do I create a message box that will appear if a field is not - Microsoft Community

hello, trying create message box appear when field populated. message reminds user perform action if date entered.  field populated using calendar, users not click on field enter data.  calendar used across database other date entries, i'm wanting box pop when 1 specific field populated.  can find how create if field left blank, not when filled. appreciated. 

curt if can find code when field blank, need negate statement not statement . . . example: sub dostuffifnotempty() if not isempty(activecell.value) msgbox "i'm not empty!" end if end sub

Office / Access / Windows 10 / Office 2013