Near field communication (NFC) is a set of standards for devices to establish radio communication with each other by touching them together. You can exchange data with other devices easily. However, Samsung Galaxy S III NFC does not work when screen is off or locked by default. It is a bit troublesome if you are a frequent NFC user. But the is a mod to hack and enable NFC on Samsung Galaxy S3 even with locked and off screen.
There are 2 versions. First = enables NFC when screen is on and locked. But it disables NFC when Samsung Galaxy S3 is in standby and the screen is off. The 2nd version lets NFC active all the time, even when Samsung Galaxy S3 is in standby and the screen is off.
Installation guide ~ How to install update zip with ClockworkMod Recovery on Samsung Galaxy S3? (Video)
Download NFC mod on locked / off screen for Samsung Galaxy S3 here.