He’s written a nice Instructable on a Temperature Data Logger that he has built and ... Clock to maintain accurate timing as well as an SD Card Module which is used to store the data collected.

[Nathan Petersen] built a Hackable Open-Source Thermostat to smooth out temperature ... [Nathan] wants to add data collection capabilities by adding some memory and SD card storage, and use ...

The 32GB microSD card is, well, an SD card that you can use ... to get the house cooled down to the right temperature before you get home. The Nest thermostat can also detect when no one is ...