I had no idea what I missing until I bought the BreatheSmart 45i. I have another brand air purifier that is basically a glorified FAN compared to this! The 45i sensor gives amazingly accurate feedback about the air quality in the room, and what I love most is the fact that the air actually smells fresh! The filter I got was the "Smoke" one because I live in a small one bedroom apartment and any time I cook, food smells linger. This quickly eliminates them. Ready to purchase a second one!