Xiaomi Auto Mode Leaves Air Unsafe for 86% of hours

For the last three years, I’ve been saying clean air doesn’t need to cost an arm and a leg. So when the Xiaomi 2 air purifier came out for under 1,000 RMB (10,000INR), I assumed it works just fine. But I had never gotten around to testing it—until now. And what I found shocked me.

The Test

Smart Air co-founder Anna ran a brand new Mi2 in the same 15m2 bedroom in Chaoyangmen where we’ve tested the DIYs, IQ Air, Blue Air, and Philips. Anna ran six tests on auto mode and six tests on the highest setting (which the Xiaomi oddly calls 最爱档 -“most love mode” or “Favourites mode”).


Anna turned the purifier on in the morning when she left home, and turned it off when she returned home, so 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 correlate highly with the US Embassy’s PM2.5 readings  (r = .90).

As in my earlier tests, I calculated effectiveness as (the number of particles before turning the purifier on) versus (the average number of particles over the last four hours).


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

Xiaomi effectiveness

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

Average % of particulates removed

Below is a normal test day. I put a dashed red line representing the World Health Organization’s (WHO) 24-hour PM2.5 limit (25 micrograms).

Xiaomi room test

The Xiaomi 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.


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

Xiaomi noise

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

Xiaomi noise vs PM 2.5

The data shows that the Xiaomi has a rather low 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. Then it turns on again when PM2.5 gets up to 70 micrograms—almost three times the limit.

Really? It can’t be kept on high?

The fact that the Xiaomi can’t be kept on continuously all night is so strange that Anna asked Xiaomi’s customer service about it 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).


How often is the air unsafe?

I calculated the percent of hours that the air was unsafe 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 left air unsafe for a shocking 86% of the time. The other similarly sized machines in my earlier tests left air unsafe only 7-16% of the time.

% of unsafe hours

Now perhaps the Xiaomi is using the looser Chinese standard for clean air of 35 micrograms. Even with that high number, 77% of the hours the Xiaomi was running, pollution levels were still above the limit.

Wait, are you sure sure?

I wanted to be really careful about this. I’ve seen other tests showing that the Xiaomi 1 works just fine, including these tests from Dr. Saint Cyr (although I’ve seen people write about flaws too, such as this guy who kept the filters wrapped in plastic, 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 (see details here).  Note however, that we did only test one Xiaomi Mi2, so there is a possibility another machine would perform differently. I invite anyone with a Mi2 to replicate my tests using the same method, and I’m happy to publish the results.

What now for Xiaomi?

From this data, my conclusion is that the fan and the filter are fine, but the Xiaomi 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 problem?

To be fair, I cannot recommend any auto mode I’ve tested. 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.

Yet I can still recommend the Philips. Why? It can stay in medium or high as long as you want, and my data shows it works fine all night 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.

Open Data

As always, I’m publishing more details on the test method and the original data for fellow nerds.


38 thoughts on “Xiaomi Auto Mode Leaves Air Unsafe for 86% of hours

  1. Hi. I am in NCR region with MI Air Purifier 2. I am willing to do a test for you but I do not have a particle counter. In case you are willing to lend a counter to me, i can do a test as per your methodology.
    PS: I am an engineer and have varied tests back in my days.

  2. same issue here. the pm sensor doesn’t seem reliable , sometime i see the number jump to 30 and fall back down… it’s always steady at 10 . well xiaomi just released a Xiaomi PM 2.5 Air Detector Portable OLED screen , it might fix things ?
    I’ve just ordered a second xiaomi air purifier . i’m going to see on how they compare, I might have a defective one
    also I find it strange that the auto on/off doesn’t work at all (schedule option on your phone)

    1. Yeah! I recently tested the Mi1 and Mi2 against four other particle counters. The results weren’t pretty. The Mi particle counter was off by as much as 200 micrograms! That’s shocking, especially when that particle counter is responsible for deciding when you need to clean the air.

      It wasn’t just high readings. It also missed on low readings. When the other particle counters were around 1-2 micrograms, the Xiaomi was still reading 9-12.

      1. I don’t think you understood what a couple of commenters suggested. The separate Xiaomi PM2.5 particle counter has the ability to control Xiaomi air purifiers. It also uses a more accurate technology for measurements than what is built into the Xiaomi 2 air purifier. A repeat test using it as the controlling device would be interesting.

        1. Aha, that standalone particle counter we’re yet to test! In the next month we’re actually going to be running a Kickstarter project to test a whole host of particle counters. This one will be in the list for sure. We’ll hopefully have results on how accurate this standalone device is in the next few months

  3. I was interested in to buy one of theses but if they always goes back to auto mode automatically after 3 hours and auto mode works so bad this machines in useless unfortionatly (I like this machine very much until I was reading this).
    This they must change, if I do not want to have auto mode is shall not switch over to that automatically!

    1. Interesting question! You mean getting under the hood and trying to code it differently? I didn’t get that technical. I just looked at the settings it has available.

      1. Paddy here, the tech nerd at Smart Air! Nice to see that there are some solutions out there, but I think for the average guy who doesn’t know Node.js like we do it might be tough to set up. Gin’s automation solution is simpler for the layman, but still not perfect. The fact that both these ‘solutions’ exist show that this is a very real problem in the first place.

    1. Hi Gin, good idea! When we ran the tests before we didn’t spot this setting. I tried this out and managed to set it up in about 10 minutes, not too bad. Whether or not we can expect the average user to do it (or more importantly know that they need to do this to breath clean air) is another issue though. I’ve attached a screenshot incase anybody else wants to set this up!

      Image: https://smartairfilters.com/en/wechatimg132/

      If you need the purifier on at other times when you’re home, or if you want to turn it off during these times, it will still require more tweaks to the settings.

      1. Paddy,

        I cannot access the screenshot.

        Kindly advise on how to keep the device running on Turbo Mode all the time.

        I have the Mi Home App installed on my Android phone.

        For everybody’s information here, I live in Delhi and on “Auto” mode the PM 2.5 estimate hovers around 60 and on “Turbo” mode it hovers around 40.

        This is not healthy. Healthy air should not have a PM 2.5 count higher than 10.

        Perhaps I should try the BlueAir Blue?

        But, I cannot put my trust in a machine that looks so cheap.

        Anyway, I have decided to stick with the Mi 2 for now.

        Any help on making it run on Turbo Mode 24*7 would be greatly appreciated.


        Dhruv Sen.

        PS: Have you guys tested the Blue Air Blue (maybe it is only available in India). How does it compare to the Mi Air Purifier 2?

        1. @Dhruv

          I’ve fixed the image link now.
          We have not tested the Blue Air Blue, so cannot vouch for it. One thing is that any air purifier that’s running during this highly polluted period (over Diwali) will find it hard t keep indoor pollution within safe levels. Especially if your room is badly sealed.

          Regarding your tests done in Delhi: we have also just tested the Xiaomi 2 in Delhi, and found that it left air unsafe 76% of the time. We will have the writeup finished soon. The Xiaomi 2 really is a dangerous machine.

          With the Blue air priced at Rs.23,000 you could get 3 Cannons for the same price. That will give you the added benefit of distributing your clean air sources around your your room, which should help counter the negative effect of leaky windows or doors.

          1. In reference to the screenshot, I am not able to access the “Automation” feature highlighted. Perhaps it is only available in China or on Apple phones, I don’t know. Your screenshot seems to be from “WeChat”.

            On my Android in India, all I have is a “Schedule Power on/off” feature that lets me set when the device shall be switched on or off. It does not allow me to select the “Favourite” or “Turbo” mode as it seems to in your screenshot.

            This is not a problem during the daylight hours when I can monitor the device but when I go to sleep the machine shall automatically switch to “Auto” mode after three hours. If I can find a way to keep it running on “Turbo” while I am sleeping, that would be quite useful.

            Please ask your testers in Delhi if they have the same features as you seem to in China. You must think of us Indians.

          2. Damn, that’s a shame! I’m on an Android phone, using the ‘Mi Home’ app downloaded from the Xiaomi App Store. Seems like this has its issues as well, so I guess we still can’t recommend the Xiaomi purifier as a reliable way of getting clean air. I hope you can find a solution and keep breathing safe!

        2. @Dhruv

          You can download Xiaomi Market from the web. You will need to change the permissions on your phone. Your phone will give you prompts to change permissions as you do so so it’s easy.

          Delete the Mi Home app you downloaded from Google Play.

          Open Xiaomi Market, and search for Mi Home and download.

          Change the location setting to “Mainland China” and the language setting to “English”. The automation setting is only available on the Mainland China setting.

          Re pair your Air purifier with the app.

          Voila! At the bottom of the Mi Home screen (not the Purifier shortcut) you will see an Automation option. Just remember you are working with Mainland China time.

          Some of it’s in Chinese. But it’s easy to workout. You can now program your purifier as suggested above.

    2. By the way, apparently Automation settings are only available if you select the Chinese Mainland server. It doesn’t matter that you’re actually located elsewhere.

      If you switch to the Chinese Mainland server, you will have to re-add the device.

      Not everything will be translated into English, but I think having Automation is worth the inconvenience.
      If you have an Android device, you can have the Chinese be automatically translated to your language https://thenextweb.com/google/2016/07/07/googles-now-tap-can-translate-text-android-screen/

  4. Please not with the “2.5ppm detector” you can set up different patterns easily, under condition you can understand Chinese. In combination with the MI Home app and the detector your problem described does not occur, you have excellent results. I could sent you screenshots how to set up. It is not difficult, if you can read Chinese at least.

    1. Aha, you mean with the standalone PM2.5 detector Xiaomi now sells? Linking up the Xiaomi with a reliable working detector is definitely one way to solve the problem. It means people will need to fork out an additional 399RMB for the particle counter (more than half the price of the purifier itself), but if you’ve already invested in a Xiaomi and don’t want to switch to another purifier, this is probably the most reliable way to make sure you’re breathing clean air.

  5. This is really interesting reading. I recently purchased the same purifier, not knowing about this problem. Then I tested it, and setting a custom speed with the iOS app, my machine doesn’t switch back to auto at all. Has Xiaomi updated the firmware since this was published? Can someone else verify I’m not crazy?

    I’m also trying to establish which behaviour is currently true of the ‘pro’ model, as I’m looking for something for a larger space.

    1. If it’s above a certain speed I’ve found that the machine does switch back to auto. However, if it’s below a certain speed, then the machine stays on the whole night.

  6. This is insane. So the air purifying is actually good but the way it deals with auto mode etc is a mess.

    What about the new Xiaomi Air Purifier Pro? I want to buy this one because I like to have an OLED display on the thing, so I can disable my wifi and just look at the device to see any problems with the air (I find it funny how people want clean air but want to leave wifi turned on all day to use the Air Purifiers that need wifi).

    This one still needs wifi to tweak it as far as I know since I see no buttons but the play is to leave it on auto mode.

    I just can’t find any legit tests on this one. It’s 500 bucks so I need to know if this works or it’s a scam. I need to find out if my leaky nose and dry eyes condition improves with clean air. My room is trapped with indoors windows that leads to the laundry so I don’t think it’s very good. Please help me choose the best air purifier.

    1. Anyone knows something more about the Xiaomi Air Purifier Pro? It’s very hard to find anything useful over the internet. Did they improve something there? Does it have same issues in Auto/High modes?
      I want to give it a try, but I’m affraid that noone has reviewed it and it seems it’s already on the market for 1 year.

  7. So the only reason one should not buy this purifier is becuase of it changing to auto mode after 3 hours?
    I have one more doubt – the Xiaomi’s website mentions that it uses a high density EPA filter and once it mentions it uses Toray EPA filter. Is that different from HEPA? i have already bought it. Should i return it? I live in Delhi. Can someone recommend me another purifier below Rupees 15k?

    1. I think the automation is now available in india as well. got to the screen where it shows the Pm 2.5 level. click the three dots on top right corner. Automation is available under general settings. My doubt still remains – the Xiaomi’s website mentions that it uses a high density EPA filter and once it mentions it uses Toray EPA filter. Is that different from HEPA? i have already bought it. Should i return it?

    2. I’m not sure on what HEPAs the Xiaomis are shipped with in India, but in China they are 95% effective filters. This is good enough for normal house purifying, so I would not worry about this. You can find information about comparisons of different purifiers on our homepage: smartairfilters.com/in/ We tested multiple purifiers in India, and found that they all perform just as well as each other even the more expensive ones

  8. The switching back to auto mode can be disabled by using the Schedule Power On/Off feature in the device settings in app : Simply set the purifier in favorites mode at desired setting and then create 3-hour intervals of power on-off timers like power on at 1200 hrs and power off at 1455 hrs and then another timer of power on at 1500 hrs and power off at 1755 hrs and so on creating a total of 8 timers and setting them to run everyday..Within every 3 hour interval, the purifier will shutdown for 5 minutes and then power on in favorites mode always, thereby preventing the switching back to auto mode which happens after 3 hours of running in manual (favorites) mode. Hope this helps my fellow Indians, especially Delhiites coping with severe pollution.

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