The disclosed computer-implemented method for protecting purpose-built appliances on local networks may include (1) identifying a purpose-built appliance that is installed at a physical site to enhance the physical site with a pre-programmed functionality and that is connected to a local network that operates at the physical site, (2) intercepting, by a router of the local network, a request from a requesting device to access the pre-programmed functionality of the purpose-built appliance via the local network, (3) querying, from the router, via an authorization channel that is separate from a communication channel used to transmit the request, an owner of the physical site for authorization for the requesting device to access the purpose-built appliance, (4) receiving, by the router, the authorization from the owner, and (5) forwarding, by the router, the request from the requesting device to the purpose-built appliance. Various other methods, systems, and computer-readable media are also disclosed.