Inside, the Halo has a cylindrical IEST-certified HEPA three-stage filter that claims to capture 99.97 percent of nano-sized particles down to 0.3 microns, but in my opinion the coolest feature is the MegaScan Particle Sensor, which continuously monitors the air in real time to detect smoke, fine dust, and allergens down to PM2.5. PM2.5, typically used as the standard measurement for air purifiers’ ability to measure and lower levels of microscopic allergens or pollutants, are tiny airborne particles that measure 2.5 micrometers or less in diameter. They are particularly dangerous because their size means they can penetrate deep into the lungs and cause serious illness like asthma, heart disease, and lung cancer.
From the purifier’s top touchscreen panel, you can control fan speed, timer, and settings. On the quietest sleep setting, my decibel monitor app wasn’t even able to pick up the noise, as the fan wasn’t perceptible above the ambient noise of my house, even when I switched off all nearby appliances. Coway claims it’s 17 decibels in sleep mode, which I believe after not even being able to hear the machine in this mode. On the highest turbo setting, my decibel reader had it hovering around 75 decibels, which is akin to running a dishwasher or a vacuum.
As part of the Airmega Halo’s sleep features (in addition to whisper-quiet functioning), it has a low yellowish night light when in sleep mode, but this can also be turned off so the top panel is completely dark. It has a light sensor and automatically enters sleep mode, dimming lights and noise level when low light is detected.
When in smart mode and it’s dark for more than three minutes, the machine will automatically enter sleep mode. If the pollutant levels are “good” for more than three minutes, the fan stops automatically to save energy. But if it detects pollutants, it will restart the fan.
It has four lights indicating air quality levels: blue for good, green for moderate, yellow for unhealthy, and red for very unhealthy. The colored lights show in a halo around the top of the machine. I found it sort of tough to distinguish between levels at a glance because this color-coding system differs from the US AQI standards of green for good, yellow for moderate, red for unhealthy, purple for very unhealthy, and maroon for hazardous.
Mixed Signals
Hopefully, you come to WIRED Reviews because we actually vigorously test the gear we recommend. I didn’t just read the specs online and flip through the instruction manual—this machine was put through some intensely bad air to see if it could hold its own.
As with all air purifiers I test, the Halo was put through testing in various unhealthy air quality situations. I used this model for nearly a month, moving around my house to test in different locations: when cooking on my unventilated gas stove, under my living room window that draws in a lot of building and exhaust fumes, and outside my cat’s litter box. Additionally, I use an indoor air quality monitor to test pollutant levels against what the machine claims.