Airthings RENEW Mode D'emploi page 13

Set it and forget it with Auto mode
You don't have to worry about when to turn Renew on or off or how fast to
run the fan. We designed Renew with a high-precision, laser-based particulate
matter (PM) sensor that keeps track of your room's air quality. As soon as it
detects an increase in PM, it activates the appropriate fan speed to keep air
quality from becoming a problem.
That's why we recommend using Auto mode during daytime hours. You can rely
on great air quality while avoiding unnecessary energy use.
Fan safe feature
If Renew detects that the fan speed drops abnormally, the motor will
automatically stop to avoid any further damage to the fan blades. This typically
happens if items are accidentally dropped or fall into the air outlet grill.
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