Xiaomi Air Purifier 2S AC-M4-AA Air Purifier White


Out of stock

  • Triple filter system.
  • 3 fan modes adjustable.
  • Control via app or button on the device.
  • Displays humidity and air quality.
  • Laser dust sensor.
  • Brightness sensor to automatically dim the display

Compared with the Xiaomi Smart Mi Air Purifier, this Original Xiaomi Smart Air Purifier 2S is improved with ultra-clear OLED Digital Display, where displays the real-time PM 2.5 index, temperature, humidity, WiFi link and working mode, allowing you to monitor the air quality of your home clearly.

Main Features:
OLED Digital Display
Clear OLED screen displays the real-time PM 2.5 index, temperature, humidity, WiFi link and working mode, which enables you to monitor the air quality of your home easily
Ultimate Triple-layered Filter
– 360-degrees barrel filter for Xiaomi Air Purifier
– Integrated early effect, three layers of activated carbon filter
– The 3-layered filter removes 99.99 percent of PM2.5 particles
– Filter replacement is very convenient when it needs to change it will remind automatically
– The suggestion of filter replacement cycle is three to six months
Smartphone App Control
You can monitor your house air quality easily through the smartphone Mi Home App, and it will provide you with more healthy suggestions to fill your home with clean and pure air
● With light sensor, the display brightness can be adjusted to dim automatically according to the environmental light change
● Working modes: favorite mode, sleeping mode, automatic mode
● Compact design, do excellent purifying job
● Low noise, low power consumption, more energy-saving

Xiaomi Mi 2 Auto Mode Leaves Air Unsafe for 86% of Hours | Review

Xiaomi automode leaves air unsafe 86% effective

The Xiaomi Mi 2 air purifier – a good cheap and effective air purifier?

Ever since I coughed through a Beijing apocalypse, I’ve been saying clean air doesn’t need to cost an arm and a leg. I even set up to provide low-cost purifiers to people around the world based on that data.

So when the Xiaomi 2 air purifier came out for under $150 (10,000INR / 1,000RMB), I assumed it works just fine. But I had never gotten around to testing it—until now. And what I found testing the Xiaomi Mi 2 shocked me.

Xiaomi Mi 2 Air Purifier: Put To the Test

Smart Air co-founder Anna ran a brand new Xiaomi Mi 2 air purifier in the 15m2 Smart Air test bedroom where we’ve tested . Anna ran six tests on auto mode and six tests on the highest setting (which the Xiaomi 2 air purifier oddly calls “Favorite mode”).


Xiaomi Mi 2 Air purifier Review and Test Results


Anna turned the purifier on in the morning when she left home, and turned it off when she returned home. That means there was no one in the home during the tests. The doors and windows were closed during the tests. (More details on the test method and all original data are here

A Dylos Pro tracked ≥ 0.5 micron and ≥ 2.5 micron particle counts during the test. Test data shows these 0.5 micron readings   (= .90).

 I calculated effectiveness as (the number of particles before turning the purifier on) versus (the average number of particles over the last four hours).


Xiaomi 2 Air Purifier Test Results

The Xiaomi purifier scored as one of the worst purifiers I’ve ever reviewed. On average, it removed only about 60% of 0.5 micron particles over the last 4 hours of the test.

Xiaomi Air Purifier Test Effectiveness Review

And oddly enough, the auto mode and the high mode results of the Mi 2 purifier were nearly identical. That’s a mystery.

Here’s how the Xiaomi results compare to earlier  using the same method, same particle counter, in the same room.


Review of average percentage of particulates removed by Xiaomi Mi 2 Air Purifier


The data shows the Xiaomi air purifier performed worse than the I’ve been showing people how to make for yet


Xiaomi Mi 2 Air purifier room test


The Xiaomi Mi Air Purifier Really Wants To Be in Auto Mode

What’s wrong? The key is that—even on the highest setting—the Xiaomi reverts back to auto mode after 3 hours. To be sure this is what the machine was doing, we put the Xiaomi on the highest setting and tracked noise levels overnight from the Smart Air Lab.


xiaomi mi air pollution test Room


You can see the noise remaining high for three hours, then it returns to the ups and downs of auto mode:


Xiaomi Mi Air purifier noise

Here is the same graph with particle counts (measured by the Dylos). The particle counts rise sharply every time the machine turns off.


Xiaomi Mi 2 air purifier noise vs PM 2.5 pollution


The data shows that Xiaomi has a loose standard for “safe.” The Xiaomi is turning off when PM2.5 reaches 40 micrograms, which is far higher than even the WHO’s 24 hour limit. And it’s far higher than   from empirical research. Then it turns on again when PM2.5 gets up to 70 micrograms—almost three times the limit.


Really? The Xiaomi air purifier won’t stay on high?

The fact that the Xiaomi air purifier can’t be kept on continuously all night is so strange that Anna asked Xiaomi customer service over at mi.com. She asked twice to make sure we’re not making a mistake. They confirmed that, no matter what, the machine will go back to auto mode after three hours. (full transcript available in the supplemental materials).


Xiaomi air purifier support conversation - blurred


How often is the air unsafe with a Mi Air Purifier?

I calculated the percent of hours that the air was unsafe for the Mi air purifier during the tests using this rule:

After the purifier was on for at least 1 hour, for any hour where outdoor air pollution was unsafe (> 25 micrograms – the WHO 24-hour limit), how many hours was indoor air also unsafe (>25 micrograms)?

The Xiaomi Mi air purifier left air unsafe for a shocking 86% of the time. The other similarly sized machines in my left air unsafe only 7-16% of the time.


Xiaomi mi 2 air purifier leaves air at unsafe levels


Maybe the Xiaomi Mi2’s auto mode is using the looser  for clean air of 35 micrograms. Yet even with that high number, it was still above the limit 77% of the hours the Xiaomi Mi2 was running.

Wait, are you sure?

I wanted to be really careful about this review. I’ve seen other tests showing that the Xiaomi 1 air purifier works just fine, including  (although I’ve seen people write about flaws too, such as   turned it on turbo mode, and the app told him his air got miraculously cleaner). So I double and tripled checked the data:


  1. We tested with a different particle counter in a different room.
  1. I re-analyzed the data throwing out any days with large fluctuations in outdoor air.
  1. I analyzed days when outdoor pollution was low to average (< 150 micrograms).
  1. I compared it to other tests done just two weeks before in the exact same room with the exact same particle counter.


None of these analyses changed the result 

Bottom Line: Performances of Xiaomi Mi2

From this data, my conclusion is that the fan and the filter are fine, but the Xiaomi air purifier has a programming flaw. Even if I use it on the highest setting, I’ll be breathing air far above the safe limit for most of the night. That’s a problem.

Is it just a Xiaomi Purifier Problem?

To be fair, I. I’ve tested the Philips AC4072 on auto mode, and it averaged 59% reductions in 0.5 micron particles, which is pretty close to the Xiaomi results. So I think this is more of a problem with auto modes rather than the Xiaomi specifically.

Philips Xiaomi Purifier Auto Mode Data Test Review

Yet I can still recommend the Philips. Why? It can stay in medium or high as long as you want, and  as long as it’s not on auto mode.

I’m confident that Xiaomi can fix this flaw by simply allowing people to run it on high without reverting back to auto mode. But until that happens, I cannot recommend using the Mi2.


Weight 3 kg




  • Triple filter system.
  • 3 fan modes adjustable.
  • Control via app or button on the device.
  • Displays humidity and air quality.
  • Laser dust sensor.
  • Brightness sensor to automatically dim the display