How do I know the HEPA 14 filter needs to be replaced?

The Air Protector One has a reminder function and notify Users when the HEPA14 filter should be replaced. From a period of time 3000 – 10000 working hours (depending on the workload), it is recommended to replace it. When the time is reached, the filter indicator light will turn red. After replacement, press and hold the filter button for 3 seconds to reset the time.