Yes, it is a bluetooth device.

They have many repositories in their github account, including the source for the apk, but also they have the [code for the web interface as well](https://github.com/ruuvi/ruuvi.gwui.html).

They provide a gateway service, but as far as I can tell, you should be able to run it all on your own network using their source code.

nullama

There is a gateway from ruuvi which you can use to do that. Obviously a little more expensive.

megaptera

opensource

Meet Ruuvi, an open source bluetooth sensor (temp, humidity, and more)

I own an H10.

Will check out the sensor. It looks like it uses BlueTooth. It would be a col exercise to write some code for my server (running Bitcoin Core) to connect to it via BT and expose that via a web interface so I could access the readings from anywhere in the world.