That is impressive! I wonder what kind of sensor it's actually using. I'm by no means an expert in this area, but indoor air quality sensors can measure a variety of aerosolized compounds as a marker for air quality (e.g. PM2.5, VOCs, CO2, etc.). To get one that would pass muster as a fart detector without being falsely triggered most of the time seems like no small feat.
Smoke and CO detector sensors I know a bit more about from prior research. Smoke detectors use either ionization or photoelectric sensors, and these days some have both (preferable for detecting the widest variety of fire types). Here's a nice summary of how sensors each works.
CO sensors can use a few underlying mechanisms as well, also summarized nicely here.
