The DS3231M breakout board is a compact breakout board for the new DS3231M high precision real time clock chip. With it, you can add timekeeping and alarm functionality to any Arduino (or other microcontroller that supports the I2C/TWI protocol).
The board comes with an onboard CR1220 backup battery (keeps time when main power is disconnected). All pins on the chip are broken out, allowing you to use extra features such as 1Hz and 32kHz square wave output, interrupt on alarm and reset.
DS3231M Real Time Clock Breakout - [Link]
Andrew Schamp has build a temperature datalogger to measure the temperature in his garden. He used a TC74 temperature sensor, 24AA1025 1024kbit EEPROM and a DS3231M+ real-time clock to record the time and temperature hourly onto the EEPROM. He also implemented a serial interface for reading the data at the end of the sampling period. The device is based on Arduino-compatible Boarduino. Every hour, the device takes a sample, and then goes to an extended sleep state, to be awoken an hour later by the interrupt from the RTC. [via]
Embedded temperature datalogger – [Link]