system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:why is it harder for weed smoke to set off my fire alarm compared to a little smoke from my burnt grilled cheese sandwich.
gpt
There are two types of smoke detectors: optical and ionizing ones. 
I don't know if ionizing smoke detectors have a harder time detecting weed smoke than sandwich smoke, so I'll focus on optical smoke detectors, which are more common in households anyway.

Optical smoke detectors have a light barrier inside of them. If smoke particles enter the detector, they reduce the amount of light that reaches the end of the light barrier. 

The smoke from your burnt sandwich contains alot of soot, which has lots of big molecules. It's pretty easy for a smoke detector to detect these. Your weed burns relatively cleanly and doesn't contain as much big particles as the sandwich smoke.