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

For the last three years, I’ve been saying clean air doesn’t need to cost an arm and a leg. I set up the social enterprise Smart Air to provide low cost purifiers to people in places like China and India to show this.

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 or reviewing it—until now. And what I found shocked me. Let me review:


The Test

Smart Air co-founder Anna ran a brand new Mi2 in the same 15m2 Smart Air test bedroom 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 2 air purifier oddly calls “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 purifier 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


That’s worse than the $30 DIY purifier I’ve been showing people how to make for years!

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 from the Smart Air Lab.




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 air purifier 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 purifier 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 Mi2’s auto mode is using the looser Chinese standard for clean air of 35 micrograms. Even with that high number, 77% of the hours the Xiaomi Mi2 was running, pollution levels were still above the limit.

Update: we subsequently ran tests on the particle counter inside the Xiaomi Mi2, and what we found was shocking.


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 air purifier, 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 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 problem?

To be fair, I cannot recommend any auto mode I’ve tested or reviewed. 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 give a good review or recommend using the Mi2.


Open Data

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

Thomas Talhelm

Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of Smart Air, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.

88 thoughts on “Xiaomi Mi 2 Auto Mode Leaves Air Unsafe for 86% of hours | Review

  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.

  9. You can always have it on high setting. Here is how to do it. Download the app and link it up to your Mi 2 purifier. You can set timers for through this. If you turn on the purifier using your phone it will go on auto mode, change it to high power mode. Then turn it off. Now turn it on and it will automatically go to high mode unless power is cut. Now you can set timers for 2hrs 59 mins. Set timer to start again 1 minute later for another 2hr 59 mins. So if you set 8 timers for 2hr 59 mins you can have clean air 24/7. I have tested with PM2.5 meter and it works.

  10. Hey,

    Your measurements show that this purifier works correctly in Auto mode. China AQI (Air quality standards) says: maximum 24-hour average 75uG/m3, Maximum annual average expose: 35uG/m3. This product is setup for this standards not US/EU or WHO which As you mention are 3 time more restricted – simple firmware update should change it easily. The question is if Xiaomi do this?


    1. We did also measure the Xiaomi against the China annual limit of 35µg/m3, and we found the Xiaomi still gave unsafe air 77% of the time! See the paragraph just above “Wait, are you sure sure?“.

  11. Im a bit new to Mi products but I just got a an air purifier 2. Mine stays on high (not turbo) as long as I want.

    I have it set to off after I leave and on before i return home. I cant choose which mode it uses during scheduling but it returns yo the last setting…so off on high /favorite turns back on to high.

    The meter seems to stay below 20 …usially 10/9 except when cooking then it reads like 90.

    So far Im pleased.

    If you have an old android. Root. Get tasker, push bullet, and remote touch/press to simulate button presses. DIY remote control anytbing as if you were using the phone yourself.

  12. First of all, excellent post. I just bought 6 of these in Pakistan, and i opened just one. Will be returning the balance 5 after reading all of this.

    My question is, if we agree that the xiaomi performs only marginally well, but at at acceptable level at the highest setting, how does the noise/decibel level at this setting compare to its peers?

    1. This is a very good question. Since the Xiaomi has only one small fan inside it, it needs to rotate at a very high speed to pull a lot of air through. This means it’s also very noisy (66dB in our tests) on its highest setting. On the other hand the Blasts we’ve created are 50dB on their highest setting, and they provide as much clean air as 2-3 Xiaomis. You can see more tests on noise in the Blast post I’ve linked to here

      1. lol if you think the xiaomi fan is small. go look at dyson. Dyson air purifier also have paper thin cheap hepa filters.

        the xiaomi filters are larger, thicker and made of several layers, hepa and charcoal.

        I’ve have both xiaomi air 2 and the dyson air purifier. i sold my dyson on ebay and purchase 2 more xiaomi air purfier 2s for the other rooms.

        They work flawlessly at removing dust and order.

        this site seems to be biased.

        1. Thanks for the concerns Andrew! You’re right, the HEPA filters on the Xiaomi are definitely bigger than those of other purifiers! I was referring to the *fan*: this is the fan blade on the top of the machine. The Xiaomi fan has a diameter of approximately 230mm, whereas most other purifiers have fan sizes much larger. You can read about why smaller fan blades lead to more noise in this post

          1. Ok – so i did NOT return my xiaomi’s. The reason is that

            a) after learning from smart air that the xiaomi’s are okay EXCEPT for that they revert to auto, i expected to be disappointed. However, it seems like xiaomi has issue’d some software update (the benefit of having a smart app) because i am able to set the xiaomi using the favorite feature to a “medium” setting coverage of 17-20m2 and this setting (and any other i set using favorite) retains itself throughout the night!

            b) yes, if there’s a power outage (which happens in pakistan) the xiaomi doesnt turn back on automatically. this is quite annoying

            c) however, considering the xiaomi’s amazing design, granular control via the app, REMOTE ACCESS (i can turn my daughters purifier at home on and off from the office) and PM2.5 level indication on my phone via the app, combined with its price, its actually a great product. (yes, the sensor sucks, but it does give an indication.)

            I REALLY think you should update this post now considering the whole basis of the post has been fixed by xiaomi.

            secondly, after reading this post, i reached out to Smart Air for some Blasts. They dont deliver the Blasts to Pakistan! Go figure.

          2. Hi Amin! Can you provide some test data demonstrating that the fan remains on that setting continuously? Of course, I’m always open to new data! However, I’m skeptical because a friend of mine claimed that she could keep her Xiaomi on high all night using the geotagging mode. We tested it (as well as the mode that turns the machine on based on outdoor AQI), and it did not remain on high. We also asked Xiaomi customer service, and they said there’s no way to keep it on high.

            Bottom line: I’m always open to new data and will happily publish any data on this question, but our newest tests (and Xiaomi customer service) continue to show that it cannot remain on the high setting.

            And sorry we can’t deliver Blasts to Pakistan! Obviously we’d love to get clean air to Pakistan, but (1) the units are very heavy, making international shipping prohibitively expensive for a single unit and (2) China Post does not generally allow shipping motors internationally.

    2. Hi Amin. Did you figure out a way to solve the issue with power outages?
      I imagine that we could use automation in the mi app (China mainland version) to ensure that the purifier is turned on at regular intervals (say every 4 hours).

  13. Can you manually set the speed to say 2/3rds of the way? Just above medium?
    Also what is the decibel reading for say medium speed? Too loud to sleep with it on? And has anyone compared this to some of the sharp purifiers (with the plasma cluster in Off)?

  14. I’m thinking of buying the Xiaomi air purifier. Anyone have one? How’s your experience? Does it reduce dust in your home? I clean everything in my home but after a few hours I see a fine dust again on all my furnitures.

  15. It seems that the problem of the auto mode was related to the sensor’s accuracy in Mi Air Purifier 2. The auto mode depends on the sensor’s information to adjust the speed of the fan.

    I saw some laser PM2.5 modules on Taobao for Mi Air Purifier 1 and 2. The feedbacks are quite positive and take the auto mode back. Even the modules can allows us to choose the CN or US standard of PM2.5 value and the high-performance mod which will send back the US AQI back to the controller.

    Here is the Taobao link for one of the modules(in Chinese), you can check it out: https://item.taobao.com/item.htm?id=549613853520

      1. For me, particle counter in Xiaomi Air Purifier Pro is accurate (tested for 33µg/m³ and 93µg/m³ of PM2.5 particles) and it goes down to 1 when air is clean. It starts to work faster definitely sooner than 70.

        Downside is that I can’t set automation based on the reads of Xiaomi, maybe it’s because of some bug, or because of EU version.

  16. I’m quite keen to buy the Xiaomi’s AP but for this auto mode problem. It seems unclear to me from above posts whether the app limitation had been fixed.

    Another workaround I can think of (which does not rely on the app) is to use a separate timer module that plugs into your power source, and then plug Xiaomi into this timer module. U can then set up 3hr power on/off cycles on your own timer module. But this assumes that the AP will revert back to its last-on mode when powered back on again. Anyone can confirm this point?

    1. Great idea Jay, we thought of this as well. Unfortunately since the Xiaomi operates like other digital devices so if you disconnect then reconnect the power it does not revert back to its last-on mode. So far the most reliable way I’ve seen (if someone insists on getting Xiaomi) is still to set up the app to turn on/off the purifier every three hours.

  17. Thank you for providing such a detailed report on the xiaomi 2. I was almost going to impulse buy it because it is so cheap. But it looks like it is worse than nothing as it is so noisy in high and completely ineffective on auto.
    I’ll save up for a better quality machine.

  18. Got a new Xiaomi 2S yesterday and then read this! Gutted. I have a couple of Cannons but I wanted something that was safe to put in a toddler’s bedroom (worried said toddler would remove the HEPA and stick fingers in the fan so I wanted a FFU). I didn’t think the XiaoMi could really be doing anything on auto mode when it was *that* quiet and your article confirmed this. However, I put it on the “most loved” mode (high I guess?) and left it on to check if it would revert to auto mode after three hours and it didn’t. It is really noisy though. Maybe XiaoMi fixed the three hour thing with the 2S? Any report on this or is my XiaoMi just a happy fluke?

    1. That’s good information Liuliu! It’s quite possible Xiaomi fixed the auto mode issue with the Mi 2S. Let’s hope so! We haven’t tested the 2S so cannot confirm. Paddy here, (the resident engineer at Smart Air!) so I’ll look into trying to get hold of a Xiaomi 2S and confirming if it’s been fixed. Be sure not to run it on sleep mode whatever you do though!

      You’ve highlighted one of the main problems with the Cannons: the fact they’re not toddler friendly. We fixed this with the DIY1.1 by putting a safety grill on the front. And of course the Blast FFUs we have now also don’t have that problem, and pack way more bang for the buck. We’re on a slow and steady path to creating more user-friendly, cost-effective purifiers that don’t have crazy high profit margins!

  19. Hello, just bought this, looking for installation on google and find this site.

    Test it for all night, mode “favorite” or “manual” displayed on app : no change.

    1. You’re right, the 2S uses a different sensor, as can be seen in this blog post (in Chinese) Xiaomi 2s sensor. The Xiaomi 1 and 2 air purifiers used a Shinyei PPD42 sensor, which was found to be fairly inaccurate by various groups. We’ll definitely try and get our hands on a Mi 2S to test the sensor in this! However, there are still two issues we need to watch out for even if the sensor is improved:

      1) whether or not the auto-mode software has been fixed to change the threshold at which the purifier turns on/off
      2) the sensor is still right next to the purifier, where air is going to be cleanest. Even if the sensor is more accurate, there is the risk that the air near the purifier is clean whereas the air on the other side of your room isn’t.

      1. I recently purchased the vax pure air 300 and I’m shocked at how unresponsive the sensor is. I haven’t had the sensor register once, not when cooking (when there was visible smoke) or cleaning (when I can see dust particles flying around). The only time I’ve seen a hint of life from the sensor is when I directly sprayed hairspray at it. I’m not sure if I’ve got a dud machine or whether these mid range purifiers all have really inaccurate sensors. I would be really interested in seeing some Xiaomi 2s tests, surely there is a purifier out there with a sensor that is at least somewhat accurate. Currently all of these auto modes seem entirely useless.

  20. As some others have said, my Xiaomi 2S stays on whatever setting i choose indefinitely.
    It also retains the chosen setting after power loss although it doesnt switch the unit back on which would be nice.

    My question for you is if the auto mode bug you found the only issue with the unit?
    If i leave it on a higher setting is it doing a good job or should i get something else?

    I would get one of your blast filter bu I am in the UAE so its not available.


    1. That’s interesting about the Xiaomi 2S Ben, thanks for the valuable info! We’ll have to test that version of the machine and post an update to the article.

      As to whether that’s the only issue with the Xiaomi: as we’ve shown, purifiers are just fans and filters, so when the Xiaomi is running on high mode it actually does a good job of cleaning the air (CADR of around 300cbm/hr, good for a room of around 40sqm). You can see that from the first three hours of data in the graphs above.

      One thing to watch out for though is that the Xiaomi is one very noisy machine when on high. It’s much much noisier than other purifiers for the same amount of clean air it delivers. And on its ‘quiet’ mode its CADR (cleaning efficiency is pretty low). Here’s a graph from our test data showing the Xiaomi on sleep mode is really ineffective, and on high it’s really very noise (and still not that effective, when you compare it to say the Blast Mini).

      Xiaomi Blast Mini CADR and noise comparison

      What I’ve heard most people do is turn their Xiaomi on low, since they can’t handle the high noise levels. This has the danger of not giving you enough clean air for your space. If you’re not sensitive to noise, and can cope with the Xiaomi on mid or high mode, then the Xiaomi is a perfectly decent air purifier!

      Also, that’s cool you’re writing in from UAE. Seems pollution there is also pretty bad, we’ve had a few people write in and enquire about getting the Blasts into UAE! We’re working on trying to do this right now, so we’ll be sure to keep you in the loop. Send us an email to global@smartairfilters.com if you want to learn more.

    1. Paddy here from Smart Air. I ran some of the tests we did with the Xiaomi! I’m glad you’ve found the information useful, we wrote this article ultimately to show people that the automode of the Xiaomi is dangerously unsafe, and to provide ways for those who’ve already bought a Xiaomi to help them breath clean air. Smart Air’s concern is that thousands of people have bought the Xiaomi air purifier, thinking that after turning it on they’re breathing clean air. We want to make sure those who’ve already bought can breath clean air!

  21. Thank You for the great review. I have just bought 2s version (unfortunately just two days before I have read this article, I am not waiting for it). I’d love to see test of this version here… BTW – I have seen readings lower than 9 on this version, so maybe particle counter is upgraded / has better calibration?

  22. No offense to this site, but I am starting to feel that “some” but “not all” of this site is propaganda to SELL MORE of YOUR air purifiers. Why is a non-professional doing these tests? How is that credible? Also, who is Patty and why don’t we ever get to meet this person? Sorry, but so far Xiaomi has been making some solid products, so unless a TRUE PROFESSIONAL?

    1. Hey John, Paddy here (not Patty!). I run Smart Air from Beijing. Here I am testing masks in London, if you want to put a face to my words:

      Paddy testing 3M mask in London

      You make some good points, and I totally agree with you. When I first started researching air purifiers, I couldn’t find any professional test data, or any results that I found didn’t have data to back up the claims. That’s why at Smart Air we started doing our own tests to verify the claims we found. More importantly, we decided to make all the test data we publish free and open source for anybody to read (check out the data to the Xiaomi tests here).

      The question that always bugged us was: if larger companies with fancy marketing appear more professional, why aren’t any of them publishing their test data? Just like you’ve said, we shouldn’t believe everything we read on the internet, but if companies or individuals back up their claims with data, then we can look through that to verify their claims. We set out to right this ‘wrong’ and publish test data for free to help more people breath clean air. If after reading this article people still buy a Xiaomi, but with this info they can fix the auto-mode issue, then our Smart Air mission has been accomplished.

  23. My last post wasn’t published, maybe because it was too long. I will try to write it more briefly.

    So far particle meter in my Xiaomi Air Purifier 2s seem to work wery well. Unlike other Xiaomi meters that You have tested here it goes below 10 without problems and displayed numbers (at least in the range 1 – 40) are close to the data from the nearest metering stations.

    Also – when I turn it on it showed 38, then after one hour on “high” it dropped to c.a. 10. When I opened the window and put my purifier close to opened window display went back to 35-40. Back into room – 10 again.

  24. After testing the mi2 purifiers (2 of them) this is the conclusion.
    The device will work all night long as long as you set the speed no higher than (22).
    If you increase speed above 22, then the 3 hour cut off kicks in, but 22 or lower seems to be working all night.
    You can test it out and share the results.
    also this is running on the current firmware, maybe that makes a difference.

    1. Not that I know of, I think the WiFi on the Xiaomi is programmed ‘on’. In fact, it’s impossible to control the purifier fully without the WiFi turned on and the app installed. Without WiFi you’d only be able to toggle between the three modes: ‘favorite mode’, ‘auto mode’ and ‘sleep mode’.

  25. Hi guys,

    Does anyone have information if Xiaomi have plans to change the Chinese standard for clean air to European standard? Changing the location to Europe in the Mi Home app did not affect the criteria when the fan speed should be increased. I am aware that I can automate the process by setting “Switch to My Favorite mode” when the PM2.5 quantity is >25mg/m3 but I was wondering if this is going to be somehow automated by the purifier itself.

  26. Xiaomi air purifier works well at a low cost. The new ones 2S and Pro do not have issue with automatically jumping back to auto mode. It is one of the best low cost air purifier on the market.

    I own a Blueair 205, Coway AP1512, Xiao mi 2s and Pro version. After reading a couple of reviews on the Xiao Mi by two folks online testing with PM2.5 detectors. They both conclude the readings on the Xiao Mi are accurate and works as described. Like Smart Airs data, the key to good air is having constant air purification. Pro version cost twice that of 2s, so if you want the best air, it means buying more 2s.

    You can read the reviews on the websites by “myhealthbeijing” and “Is It Worth to Buy | Xiaomi Air Purifier Pro Review” from stiwe website.

    Pros are low cost, relative cheap filters, works just as well as expensive units with, packed with features

    Con louder than competitors on medium and high settings

    1. Great writeup Joe, you’ve hit a lot of the main points! The biggest concerns we (Smart Air) had with the Xiaomi when we were testing it is the fact that the auto mode was giving dirty air most of the time. If they’ve fixed this in recent models – as we suggested in this post – that’s great news, and we’ll need to go out and test it! If they’ve upgraded the particle counter inside the Xiaomi, that’s also good news, although that doesn’t necessarily mean the Xiaomi will be work more effectively to clean the air. More data is needed!

      The Xiaomi has definitely done a great job in lowering the price of clean air, the one concern is that it might not be providing clean air in a reliable and trustworthy way as we expect. Unfortunately most people won’t read blogs like this, so won’t know what they need to do to make the Xiaomi work well. That’s what concerns us the most! You’re spot on that the noise levels of the Xiaomi can be considerably higher than other machines, this is another problem in itself. If the purifier is too noisy, we won’t turn it on! Or we’ll turn it on to ‘sleep’ mode, which we’ve found to be very ineffective. Once again, people will be expecting to breathe clean air whilst they might not be.

  27. Hi all. I currently have a Cannon, a DIY , a Xiaomi 2S , and I just got a Xiaomi Pro. I never had any problem with the 2S switching itself to auto mode (which is why I felt confident getting another Xiaomi). The Pro, however, immediately started doing so about every hour or so. I read through many of the comments here but I didn’t see much info on the PRO or many recent updates on the 2S. Has Xioami completely fixed this problem in the 2S or am I just really lucky somehow? And more importantly, what about the PRO? If it is going to do this constantly, I will return it.

    I know that it can be worked around to some degree via automation, but I shouldn’t have to write code for my own product and I have found the automation implementation to be hit and miss on the 2S. Thanks in advance for any help

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