If you’re a heavy NFC user then you may want to keep NFC active at all times. The Galaxy S3 turns it off if the screen is off. So in comes XDA.
There are two versions. The first just enables NFC, when screen is on, but it also worked when it is locked. Also with a PIN or Password-Lock everything is fine. But it disables NFC when the SGS3 is in standby and the screen is off.
The second version let NFC active all the time, even when the SGS3 is in standby and the screen is off.
Nothing else is changed in the behavior of the NFC.
Over at TheUnlockR they’ve put together a step by step on how to install this mod so check it out.