Their old one had an issue with the dust sensor clogging. The new ones use the Honeywell sensor. It has a tiny fan on it (inaudible in a quiet room from 5 inch

Their old one had an issue with the dust sensor clogging. The new ones use the Honeywell sensor. It has a tiny fan on it (inaudible in a quiet room from 5 inches away); mine ran well for a couple of years until I knocked it off my desk. After that, the fan started rattling, so I ordered another Honeywell sensor ($40) and replaced it (no soldering required, just a screwdriver). That sensor's datasheet doesn't have any cleaning instructions, so I don't think it's a big issue.