First thing I noticed after unpacking: While the included manual only talks about the USB connection in terms of providing power, the thing actually enumerates on the bus as a HID with vendor/product ID 04d9:a052.

When researching this VID/PID combination, I found that the device appears to be sold in other markets, with different brand markings: http://habrahabr.ru/company/masterkit/blog/248403/. I don't speak any Russian, and Google Translate is rather weak here, but from the pictures it seems that someone was using an identically looking device to monitor some brewing process. And that there's software that reads the data from USB.

Doing a Google image search for co2 meters and selecting a product photo that matches the physical appearance (with yet another different branding) lead me to this American company which had not only the Windows software to connect to the meter for download, but also a PDF documenting the protocol. Well, this should be a breeze …