Chop peppers, onions, and garlic. Layer them in a quart size mason jar. Pack them down as tightly as possible.
Warm water + salt on the stove just enough to dissolve salt. Cool to room temperature.
Add room temperature brine to jar and cover ingredients with a fermenting weight or something that can hold the contents under the brine.
Cover with a lid. I use a fermenting lid (or a pickle pipe) you can use any regular lid, but if it's not a fermenting lid, you will have to open it daily to let the pressure off.
Leave to ferment. I like the flavor of 5-7 days. You can go as little as 3 days, or as long as 2 weeks
Over a bowl, strain the contents through a strainer and set the brine aside.
Add solid contents to a blender and add 1/2 cup brine, plus the juice of a lime.
Blend and assess consistency. You can add more brine to make it thinner if you like.
Run through a food mill. This step is optional, but I like to run my hot sauce through a food mill to strain out the bulk of the seeds and skin. The result is a thinner hot sauce. You can skip this step if you prefer a chunkier hot sauce, it'll resemble more of a salsa consistency, with a hot sauce flavor of course.
Store in an airtight container in the fridge. Shake before use.