This tiny RTC Real Time Clock DS1307 I2C IIC Module is perfect to be used with Arduino and other microcontrollers. It contains a DS1307 real-time clock IC with a backup battery. It’s one of the easiest to use RTCs out there, with Arduino and other libraries or simply use I2C commands to set and retrieve the time and date. Includes a lithium coin cell battery which should be good for four years at least.Along with the DS1307 real time clock, this RTC module also has an Atmel 24C32 EEPROM chip which is handy for storing data without worrying about power loss. There is also space on the board to solder your own DS18B20 temperature sensor.This battery-powered clock allows you to keep a reasonably accurate time even when your Arduino is powered off.  It is very useful in data logging and other time-sensitive applications. The device uses I2C to communicate with your Arduino.