Preheat your oven to 250 F/121 C. Line a rimmed baking sheet with foil, and spray the foil with nonstick cooking spray.
Cook the bacon in a skillet until crispy, then drain off the fat and let it cool. Once cool, coarsely chop the bacon into half-inch pieces.
Place the bacon, popcorn, and chopped pecans into a large bowl and toss them together.
In a small saucepan, combine the brown sugar, butter, and corn syrup and stir them together over medium heat. Once the sugar and butter have melted, stop stirring and insert a candy thermometer.
Continue to cook the sugar until it reaches 238 F/114 C on the candy thermometer, which should only take 3 to 4 minutes.
Once at the proper temperature, remove the pan from the heat, add the baking soda, and stir vigorously. The sugar mixture will foam up, so be careful during this step.
Pour the foamy sugar over the popcorn mixture in the bowl and quickly stir everything together, making sure the popcorn, nuts, and bacon are coated with caramel.
Spread the popcorn out on the prepared baking sheet. Bake it for about 45 minutes, stirring every 15 minutes to distribute the caramel.
Once it is golden brown and crunchy, take the popcorn out of the oven and allow it to cool completely. Store bacon caramel popcorn in an airtight container at room temperature for up to a week.