I am trying to do something like =IF(A110,RunMacro). I realize that
this cannot be done but there is a generic syntax that will basically
do this:

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
If Not Application.Intersect(Target, Range("A1")) Is Nothing Then
If Target.Value 10 Then
MsgBox "Put Your Code Here"
End If
End If
End Sub

The trouble I'm having is that the message box does not appear if I
type "11" in A1 and press enter. The message box only appears when I
click back on A1 after having already typed "11".

Am I missing something?