I recently realized that we had a "smart" thermostat installed. I don't need to change the temperature from my phone, so I turned off the internet connection to it.
What's weird, is that it previously had a big delay after pressing a button to change the temperature one degree, press again, big lag. After I turned off the internet, there's suddenly no delay.
So I don't know who it was trying to send that info to, but it's a little creepy.