Message if duplicate found

to a sheet module

Private Sub Worksheet_Change(ByVal Target As Range)
With Target
    If (Not Intersect(.Cells, Range("A19:A82")) Is Nothing) * _
       (Not IsEmpty(.Value)) Then
       If WorksheetFunction.CountIf(Range("A19:A82"),.Value) > 1 Then
           MsgBox "Duplicate"
           Application.EnableEvents = False
           .ClearContents
           Application.EnableEvents = True
       End If
    End If
End With
End Sub