I've come to find that "smart" as in, I can schedule them, is quite useless in the long run.

In the last 3 months:

1) Lennox "Smart" icomfort thermostat... tasked with running the entire dual-mode heating and cooling system in the house (ie: all the heating and cooling). Hard reset itself and lost it's cloud connection. Was still showing in the app (ie: no option to add a new one), but the app wouldn't relay any information and the thermostat itself was showing "cannot communicate" error when trying to make any changes to the temperature settings. Buried deep in the installer settings menu was an option to re-pair it, where after several obscure errors, it finally re-joined the "account" and resumed proper working. The worst part is that this thermostat is basically doing the exact same thing as a normal thermostat, with no added intelligence (sensing temperature and turning relays on/off).

2) Wemo's randomly disconnecting from the app, despite google being able to control them... this is particularly concerning as they're clearly connected to something.

3) Wyze camera (v3, latest firmware...) that will run fine for months on spotty wifi (I've added an SD card for local loop recording) but the if you try to connect to it from within the app for live viewing, and it fails to negotiate a connection (due to the aforementioned spotty wifi connectivity), it will permanently disconnect itself.

4) Wyze smart irrigation sprinkler controller that is weather forecast aware, opting to skip watering if mother nature is planning on doing it anyway... will skip a watering due to forecasted rain but not check if it actually rained when calculating ground humidity levels, therefore skipping the next one as well. There is also no way to connect two sprinkler controllers (if you have more than 8 zones) in a group so that they don't run simultaneously and exhaust water pressure. They are considered 2 separate houses.

5) Meross smart garage door controller will occasionally forget whether it is open or closed, and displaying "overtime" warnings accordingly and will wait for 1 minute after a close/open command before recognizing its true state by process of elimination, "I've been closing for a minute, so now I'm closed". Bafflingly - it has an integrated magnetic sensor on the door to detect when it is actually open and closed - it knows when the door is opened by a 3rd party, and alerts accordingly.

6) Blink cam will trigger its own motion detection when it's turning on or off it's blue "recording" light, causing an infinite loop of "motion detected".

My dumbest smart house items (LED lights mostly, some bluetooth with wifi hub, some built-in wifi) are the chinese ones you see all over Amazon, and they tend to "just work" in their dumbness. They all use one of 2 apps (Smart Life or Magic Home - amusingly, most work on either since they likely all use the same wifi and control ESP). They rarely disappear, work without firmware updates, and I've yet to catch them sending anything back to the mothership (ALL smart devices are on their own wlan & subnet without packet forwarding - I would recommend everyone do this). You can pair them with Google Home, Alexa or Siri, and then get rid of the app itself if you are concerned. Many of them can be connected to simply by setting them into pairing mode, connecting to their wlan, and hitting an http api or sshing in.

I have high praise for the lutron "caseta" family of smart lights and plugs - which use a proprietary radio and a single control hub which never disconnects and doesn't pollute the wifi radio space. The only downside is that they cost more than the wifi-integrated plugs, which is a bit crazy given it's a low power zigbee-like radio and control plane.

Hopefully things get better before more critical things become "smart".