It’s an air filter with an actual filter that can be replaced. There is an indicator light to alert you. My only complaint is that the power button will still emit the blue glow in the dark without the night light option selected (the outer circle glow in the photo). But, we slept with it on overnight and I felt less congested and more rested in the morning - a win. I don’t know how long between filter changes (*says 3-6 months) or where to purchase a new filter or how much that is... but, there is a website and customer service phone number included in the manual.