I imagine probably 99% of them are but I don't have any research to actually back that up.
They’re also not networked, so an adversary would have to get into range, making a potential attack much more complicated. It certainly won’t defend you from a targeted attack, but it will keep $random_person_on_the_internet reliably away and I don’t have to rely on $companies server/network security.
"We begin by coveting what we see every day... Clarice"
Many of the smart ones both broadcast like the dumb ones and, separately, send a signal on wifi to a central server for online viewing, so they fully incorporate the problems of the dumb ones.
And as of right now, the only 2 things that go through that firewall are the nest thermostat (yeah, it's pretty and hasn't given me any trouble, so i'm happy with the tradeoff here), and the google homes (again, another tradeoff myself and my family are comfortable making).
Everything else is on that network without access to the "internet" directly, with WPA2 encryption for protection against local eavesdropping, and pushed through an open-source home-automation controller called "Home Assistant" running on an intel NUC served up over HTTPS to our devices.
I don't have any baby monitors yet (no babies!) but we do have cameras and with this system they work great and I sleep pretty well at night knowing it's all secure enough that i'm happy buying cheap devices knowing the security is garbage.
Most of them will output standard formats and streams that you can hook into in my experience (but i might be inadvertently selecting for those)
Get a new device, plug it in to a locked-down network that passes all packets through a deep packet inspector connected to some ML. Add in proxy features so if the vendor turns off their service, your personal network MitM can mimic the server on the other side.
I doubt this is feasible due to the fact that consumers clearly value "it just works" (implying simplicity/less security) over secure/private. (And probably a bunch of other factors I'm not thinking of.)
https://www.amazon.com/Sony-BabyCall-Receivers-Discontinued-...