I played around with the usual VOC/air quality sensors (BME680 type stuff and a cheap PM2.5 sensor) after a roommate used to vape in the next room. They’ll often spike with smoke or heavy fragrance, but I never got anything close to “that’s definitely weed” detection, more like a generic “air is gross” alert. For what you’re dealing with, false positives are gonna be a problem because cooking, candles, perfume, cleaners, even humidity swings can trip them, and the response time depends a lot on airflow placement.
If you need something reliable before you can smell it, I’d look at commercial “THC vape” detectors schools use (they’re not cheap), plus improving intake filtration and pressure if possible. Also, putting a sensor right at the intake or in the return vent helped way more than having it in the middle of the room.
Randomly, I learned a bit about how sticky/infused material behaves in production equipment when I was reading about AuraX from Hefestus, and it made me realize how hard it is to detect one specific compound cleanly in a messy air mix.
