I’ve been using a cheap Aqara temp/humidity sensor in my fridge for years. Works fine, as I said. Many others do the same. There’s a lot more plastic in fridges than you might expect.
My ZigBee devices use an ethernet based coordinator which communicates with my Home Assistant install via MQTT. The coordinator software is called Zigbee2MQTT. The coordinator does not send any data anywhere except Home Assistant.
There are many easy ways to keep your data local and private while still allowing notification when you’re away from home. In my case, I pay $65/year to Nabu Casa to access my Home Assistant when I’m not at home.
I use a very similar setup to keep an eye on my mom’s place from 500 miles away, including many sensors and multiple camera feeds, which are also local only with no cloud component. Frigate NVR is installed as a Home Assistant add-on, which runs detection on each camera feed and records clips when a person is detected on any feed and also pops a notification at the same time. If she wants to save a clip, she can download it, otherwise it’ll be deleted after 5 days (configurable).
There are other ways to get access to local data remotely. If you don’t want to pay for Nabu Casa (which funds Home Assistant development), there’s also Tailscale/headscale, ZeroTier, Cloudflare, DuckDNS, reverse proxy, etc.
You could also just have Home Assistant send you an email when an event is triggered, like a rise of 2 degrees in your fridge in an hour, or a drop of 20% in energy usage over 30 minutes.
Or you could just have a notification pop in the Home Assistant app on your phone, which will work remotely with most of the methods I just listed.
EDIT: Didn’t respond to your last paragraph:
I get that you’re very afraid of the security implications of iot devices, but none of the ideas you’re proposing are actually solutions to the problems a truly connected device can solve.
I’m not “very afraid”, I’m simply aware of better alternatives. Why would I risk the security of my network by giving Samsung or GE or LG a backdoor into my network when I can get most of the same information their app can give me by using cheap sensors and Home Assistant?
Depends on the fridge, in my opinion. I don’t need any door sensors because my fridge will beep at me if I leave a door open for 12 microseconds, and the freezer is pretty reliable, it’s just the fridge that needs adjusting from time to time.
I just use a ThirdReality smart plug with energy monitoring primarily so I can see power consumption, but I still contend that this combined with the temp sensor is enough to let me know if there’s a problem when I’m not home.
Also a 20 year IT person, but on the Linux server side. I do have an isolated network for IoT things that don’t have local alternatives (pfsense hardware firewall, 24 port managed switch in the rack and ruckus APs), but I hate (hate) the enshittification of perfectly good hardware with software that exists solely to harvest my data so a corporation can have an additional revenue stream for the shareholders, and I will go pretty far out of my way to avoid giving money to companies that do this. Dreading the day my beloved dumb LG plasma TV dies.
What hardware are you running your HA instance on? Mine runs in an HAOS Proxmox VM with the USB port for the zwave dongle (for the locks) passed through. ZigBee coordinator is ethernet, so it’s just plugged into a switch in the living room.