AFAIK there isn't any sensor, the filter guide is just based on the length of time it's been running (possibly factoring in the fan speed?)

How often it will need cleaning will ultimately depend on the environment. I was worried it might be prone to suck up dust / hair but it's far enough off the ground and the fans aren't so powerful that I don't think it's really an issue to worry about. I expect when it tells me the filter needs cleaning it probably won't and is just designed for worse-case environments.

The fans are kind of gentle, not like the kind on Bitmain or even a traditional fan-heater.