First, not all HA systems have to be on a network, and the certainly don't have to be on an Internet-connected network. It really depends on what HA system you're thinking about using. For instance, you could do a lot with an Elk-based system without any IP-based network at all. Or you could do a really complex IP-based network, but put it on an isolated network without Internet access. Or a separate network with a locked-down firewall between the HA network and your home network.