Nexus used the Bus Pirate with an MCP9800 temperature sensor and documented it on the wiki:
The MCP9800 is an inexpensive, high-accuracy, 2-wire (I2C) temperature sensor. It features selectable 9/10/11/12 bit resolution with a typical accuracy of ±0.5°c at 25°c, programmable alarms, and low power consumption.
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