My smoke dectector doesn't like bacon!

I put a quart sized zip lock bag over ours when I cook bacon. Slides on easily and it stops that racket until after breakfast. Our detector is next to the steps upstairs so I can reach it with no problem. And since it is in clear sight of the living area, we don't forget to remove the bag.
I posted a picture of it on here somewhere but I can't find that post now.

Why is it only when we cook bacon????