Any owner of the New 3DS understands the paranoia of accidentally hitting that external power button and turning off your 3DS. After accidentally turning my 3DS off while playing Pokémon and losing a Battle Maison streak, I had enough lol and designed my own button that absolutely can never be hit by accident. You can press it with a pinky fingernail, pressing over the opening really hard with the pad of a finger, or using the tip of your stylus. (I use my pinky nail.)

I only have an XL model so can't promise it will work with regular size, but I would be very surprised if the components involved are different. (If someone has a regular-size New 3DS and wants to try this out, I would love to hear if it worked!)

If printed with FDM, MUST be printed with button surface face-down on the plate, EXACTLY as oriented in the STL, with as much detail as your 3D printer can manage. This orientation is mandatory because the features of the side of the print facing the interior of the 3DS are very small and precisely shaped. Sanding the button surface smooth before installation is suggested for a clean finish.

~~HOW TO INSTALL:~~
You will need: tweezers, a 00/2mm Phillips screwdriver, and a flat-head screwdriver or spudger

1. Remove the game cartridge, if you have one in the 3DS. Unscrew the two embedded screws keeping on the battery panel. Then remove the battery and SD card.

2. Remove the screw covers with the flat-head screwdriver or spudger by wedging them underneath. They're held on with adhesive. Be careful you don't damage the soft rubber as you unpeel them and pry them out of their little holes.

3. Remove all of the screws attaching the backplate, then carefully lift the backplate from the bottom and let it "hinge" open-- the shoulder button connectors are connecting the back plate to the rest of the 3DS. Be careful not to tug on them.

4. Remove the membrane covering the power button and the plastic power button itself. Set them aside in a safe place in case you ever want to go back to the original power button (not pictured here because I don't remember where I put mine lol.)

5. Hold up the 3DS on its side in one hand so the power button opening is facing down to your work surface (eg table or desk top.) The membrane doesn't fit over our 3D printed power button, so we need gravity's help to keep it in place until we close the 3DS up again. Hold the 3D printed part with your tweezers in your other hand and orient it as shown in the picture. (EDIT: Looking back at this I can't remember if that's actually the correct orientation or if it's backwards in the picture, you might need to turn it around the other way, I don't feel like taking my 3DS apart again to double check lol.) You might need to jiggle it around a bit until it's fully seated-- it will fall into place.

6. Keeping the 3DS held up vertically so gravity keeps the new button in place, rotate the main body down like it's on that "hinge" and fit it back against the back plate. Once they're snugly fit back together, you can put the 3DS down again.

7. Screw the back plate back into place, then replace the SD card, battery, and the screw covers (screw covers optional, I keep mine off so I can open my 3DS up again easily to fiddle with it lol.) Replace the battery cover, then done! Enjoy the peace of mind!