Tip: how to become an ‘outsider’ easily.
Marcus Roskosch gave me a clever tip, in the help file of his NetworkToolbox or NET-Toolbox iOS app. If you have a device that has a 3G/4G network interface, connect to the internet using that interface only, which probably means switching off wireless LAN interface temporarily so that ‘wifi’ is not preferred. Your device will then have IP address(es) that are outside your normal home network, so this gives you the quick easy ability to look at things from the outside, to do security checks that you cannot normally do as a LAN insider. If you use iOS, the NetworkToolbox app can do various tests from outside looking in as well as inside your LAN, the former being the most important, clearly.
Obviously you could otherwise get a friend who is an outsider to do this, but this is just a quick tip to allow you to test things on your own.