[mrb]

Given that this image: https://cdn.prod.website-files.com/653a9fbd1075088b6c8f8bd3/... shows PM2.5 and CO2(ppm) it may imply they monitor particles and CO2 levels. My guess is it also monitors humidity, and temperature. Humidity helps distinguish smoke from water vapor (eg. steaming shower).

CO2 sensors are generally pretty accurate, but PM2.5 sensors are notoriously prone to false spikes usually caused by dust in or around the sensor: https://www.reddit.com/r/Awair/comments/10r1uyo/inaccurate_p... or https://forum.airgradient.com/t/unusual-pm2-5-readings-on-ne... or https://community.purpleair.com/t/what-to-do-about-incorrect...

My guess is it's likely a sensor in a hotel room accumulates dust over time, leading to high PM2.5 measurements maybe when something (eg. suitcase) bumps against the case, shaking the accumulated dust and releasing it around the sensor.

[boothby]

Note that pm2.5 will also spike when you've used shampoo, perfume, deoderant, lotion, sunblock; if you use dryer sheets and you unpack your clothes, etc.

[paradox460]

Farts will cause it to spike

[winrid]

It's unfortunate that we can't comment on reviews.

[mrb]

Exactly! So many ways to make PM2.5 spike. I didn't even know about shampoo and sunblock. I assume for sunblock it's the spray kind?

[billyjmc]

This is news to me, but I’m unsurprised. Why people use so much strongly scented products is absolutely baffling to me.

[veeti]

I wonder if you could set it off by farting too much: https://www.youtube.com/watch?v=zvB0wRFebus

[microtherion]

That's awesome for the hotel! The less they dust their rooms, the more "smoking fees" they can charge guests.