Provide warning when chartacer count reaches 250 count

I'm trying to provide an audible and message box alert when the user reach a character count of 250 characters in a text box with 255 characters max.

Here is my code but is not working:

Private Sub txtUpdate_Change()

Dim lngNumberOfCharacters As Integer
Dim Update As String
lngNumberOfCharacters = Len(Me.txtUpdate)

    If lngNumberOfCharacters = 250 Then
    DoCmd.Beep
        MsgBox "You have typed 250 characters and the limit is 255 characters."
    End If

End Sub

Select allOpen in new window