I haven’t got into this yet, but the approach I was going to look into was using an IP camera and CCTV style software, which gives me my buffered recordings. I can then choose to process the image for motion, or use a PIR or push of the door bell to trigger the save (which is less intensive processing).

I did some work on locking down an Android tablet, found it quite hard to do. With CDNs etc in play, the IP ranges that need to be opened are quite vast and generic (i.e. lots of cloud providers that host half the Internet).

I used Squid HTTP proxy for URL inspection, but still, many generic domains being connected to. And I found whether an app, including some Google system ones didn’t always respect the device’s proxy settings and would simply fail.

For TVs, I’ve kinda gone meh, and isolated them from other devices, but given them Internet access.

Completely disconnected from the Internet means that packets can’t make it from the device to the Internet. You achieve this through physically separate networking, VLANs or simply relevant firewalls. With a stateful firewall you can get picky with restrictions on TCP SYN packets to get fine grained control of who can establish a connection. I felt this level of detail was inappropriate for OP’s self proclaimed technical proficiency.

Possibly OP means Internet connected, but not using a third party service to handle the feed. If they do, then they can ignore my comment and select something more appropriate from other helpful contributions.

Just buy a conventional webcam/ipcam and use that in addition to a conventional doorbell. If you’re not wanting it to be Internet connected, you aren’t going to be using away from your home.