Using VBA to error check multiple cells

I'm extremely new to VBA but need to use it to complete error checking, consisting of just a popup message, for an excel spreadsheet. Looking through the forums I found a code that works for one of the cells, but i need it to work for 100 cells (in a single column).
The code is:

Private Sub Worksheet_Calculate()
If Me.Range("I3").Value = 1 Then _
MsgBox "Invalid value"
End Sub

I was hoping someone could alter this to allow for I3 - I100, any help would be appreciated.

Moderator's Edit: I added code tags for you since you are new to the forum. Please read our rules and adhere to them in the future.

Try this instead:

Option Explicit
Private Sub Worksheet_Change(ByVal Target As Excel.Range)

    If Target.Column = 9 Then
        If Target.Value = 1 Then
            MsgBox "Invalid value"
        End If
    End If
End Sub