It’s finally here, ntrboot!!!! This allows us to reflash the flash of an AceKadr2i or R4i Gold 3DS RTS to allow for simple installation of Boot9Strap to any 3DS with the help of just the card and magnets. This also allows you to unbrick any 3DS bricked by normal means (Not Bricks done by Gateway). The Bootrom of the 3DS checks if Start+Select+X is held down and the shell closed.
If these requirements are met, it will boot, straight from the bootrom, a specially prepared NTR cartridge. This gives those cards bootrom access. But where does the magnet come into this? Well, you can’t really press Start+Select+X if the lid is closed so if you put a magnet on a specific position on your 3DS the 3DS will go to sleep mode. The best thing about this booting straight from bootrom is that the card get’s booted before the 3DS checks the NAND or anything else. This allows you to boot even if you have a bricked NAND, install Boot9Strap, then boot Decrypt9WIP and reinstall the Firmware. And voila, there you have a fully working 3DS again.
https://twitter.com/hedgeberg/status/896256780552089600
If you own an Acekard2i or an R4i Gold 3DS RTS and would like to install this you can find an excellent guide over at 3ds.guide detailing the full installation procedure.
With this, the last fortress of the 3DS has pretty much fallen. This is compatible with every 3DS, and 2DS (Yes, also the new2DS) and easy to install without soldering anything. I bet soon some people will also start selling preconfigured ntrboot cards for people who wish to easily install CFW to their 3DS or new people offering CFW installations since the whole procedure is fully brick-proof now. And even if you brick this lets you revert the brick with ease.
Source: Hedgeberg