A big thanks to Aaron Christophel aka atc1441 for his work in making this possible!
I picked up 4 of these Low Energy Bluetooth sensors from Aliexpress for $4 a piece when they are on sale. I was surprised by how fast I received them from China, only 3 weeks!
My goal was to add these into Home Assistant, but I needed to get a Bluetooth dongle first. This one from Amazon worked well under Linux and passed through Virtual Box to my Home Assistant VM with no issues. https://www.amazon.ca/gp/product/B07V1SZCY6/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
I had to install a custom component to scan and detect the device, but first I wanted to install the custom firmware so I would not need to worry about encryption keys etc. Aaron’s Telink flasher could give you the keys and information if you wanted to keep the encryption.
I had to first use my PC to flash the custom firmware as my iPhone and MacBook would not work properly. Lucky I had a new Bluetooth dongle to use.
The repo page has a good write up on how to install and links to his online over the air (OTA) flasher that works well. Watch his video and give him some likes!
Telink Flasher for Mi Thermostat
You will need to install the custom component in Home Assistant via HACS. Here is a link to the repo with instructions to install. Pretty easy f you use HACS. I did not need to do anything else as Home Assistant detected the dongle and Passive BLE Monitor did the rest.
HACS Custom Component Passive BLE Monitor