he PCF8523 RTC module from Adafruit is Real-Time Clock (RTC) and calendar optimized for low power consumption. Data is transferred serially via the I2C-bus. Alarm and timer functions are available with the possibility to generate a wake-up signal on an interrupt pin.
The PCF8523 has a built-in power-sense circuit that detects power failures and automatically switches to the backup supply. It can be used in many applications such as data logging, clock-building, time stamping, timers, calendars and alarms.