Diagnosis
The color indicator is driven by the particle sensor, not a gas or odor sensor. Blue means low particles, so it might not detect smells like smoke or VOCs unless they come with visible dust.
How to Fix It
This is working as designed. If you want it to respond to odors, you need the optional Customized Filter for odors (like the Pet Allergy or Germ Defense filter). Also, make sure the particle sensor on the front is clean—wipe it gently with a dry cloth.
If That Didn't Work
If you have the odor filter and it's still not detecting, the sensor might need recalibration. Run the purifier on Auto mode in a known-clean environment for 24 hours to let it baseline itself.
Heads Up
The auto mode bases fan speed on particle count, so for odors, you might need to manually switch to a higher speed or use the "Odor" setting if your model has it.