Mh, yeah I see the possibility of using an open network in theory, but in practice I haven't seen a open Wifi network in years (excluding business owned ones, but usually you need to confirm something there and can't use them forever). So not sure how feasible that is. The more sinister option is done by Echo devices for example (that: https://en.wikipedia.org/wiki/Amazon_Sidewalk), but also requires a second device nearby. Much more possible possible though, if similar devices are nearby. But that can't be hidden anyway and it should be possible to check for that.

I feel like the best option to get the monitor network connected is still a secondary device and never using the built in firmware (and first checking if said device got things like you described).