Additional Nest Thermostat Data?

Is the current Nest Thermostat pulling all the available data, or can more things be read by HA with some tinkering? Mostly interested in what the Nest considers outdoor temperature to be. My HVAC system is such that my heat pump runs until it’s -1C (or whatever I set in my Nest) outside, and then my propane furnace will kick in. So I’m interested in tracking when that happens.