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]
So I ordered a 1-Wire RTC (real time clock) from the maxim corporation. To be exact its a ds1904. What is really cool about the 1-Wire protocol is it only needs 1 wire to send data on. It is a bit misleading however since it does need a ground as well.
1Wire Real Time Clock With Arduino - [Link]
This project named “Kid-e-log” combines an Arduino, EEPROM, RFID reader, real time clock chip and LCD readout to keep electronic tabs on the kids by having them clock in and out of the house with RFID cards. Source code is included. [via]
RFID Arduino punchclock - [Link]