This is a Mini Real-Time Clock module, it design for Raspberry Pi, but it also can be used to Arduino.
Pluging it into Raspberry Pi GPIO interface, and all is ok. This is the easiest way to keep it in time.
Work in 3.3V and 5V
Supported Raspberry Pi and Arduino
Compatible with Raspberry Pi A+,B,B+/2.
DS3231 RTC IC
Self-adjust 3.3V and 5V
Size: 14x14x12 mm