[philjones]

They're using the battery temperature run through an algorithm they've devised which they've found to, when averaged with other local users, estimate the actual temperature. My phone's been charging since I installed the app and that skyrockets the battery's temperature, so I have yet to see it give a remotely accurate reading of the ambient temperature.

[brendan_gill]

Yes, this is how we do it. It's going to be quite rough for an individual user for an individual moment in time but we've shown that averaged over many users that battery temperature is closely correlated with the ambient environmental temperature. You should see greater accuracy when your phone has been relatively idle and reached an equilibrium with the environment whereas if your phone has been whirring through cpu cycles the accuracy will decrease.