In-Depth Review: Wynd Halo 1st Edition Sensors

The Wynd Halo 1st Edition uses a proprietary PM sensor with a blue-light laser instead of a red-light laser, which presumably makes it more accurate and precise. Interestingly, I remember during the Kickstarter campaign of the monitor, backers were asking the company if they will sell the sensor as a component part to third parties, and they said yes because it was about to revolutionize the industry.

Although I don’t have a reference monitor, the comparison I conducted is considered a field evaluation in a real-life situation. AQ Monitors are designed to operate inside apartments and buildings for this reason I personally value more a field evaluation in situ than a lab evaluation where every parameter is controlled.

This kind of evaluation won’t tell us how accurate is the sensor, but it will reveal the correlation against other monitors in order to determine if measure something respectable. For example, there are many field and lab evaluations for the commonly found Plantower PMS5003 sensor that demonstrate a correlation of 0.78 – 0.93 against various reference monitors.

I had the devices running side by side for 2 weeks. I picked a date randomly, but I made sure humidity didn’t surpass 70% to avoid hard interference and although I had thousands of measurements, I ended up creating 1-h average values for all the parameters to avoid time inconsistencies. Some monitors take measurements every 10 seconds, others every 5 minutes and others every 15 minutes.

Thanks to the free software RStudio and some packages I ran various Pearson correlations tests between four monitors. I am not going to reveal the name of the competitors only the sensors they use.

It is important to know which sensors are used in order to make the right conclusion in the end. The numbers we see in the table below help us understand better the correlations. Numbers closer to the value of positive 1 mean that we get the best correlations. Negative values indicate that both variables move in the opposite direction.

(1) Although they use the same VOC sensors by Sensirion, the results are different. I think this is a design issue, in particular, the VOC sensor inside the AQ2 gets hotter than the normal as it is placed under the CO2 sensor, as a result, the readings are inconsistent. 

(2) It seems to me now that AQ3 has an issue with the temperature sensor as across all the correlation results it scores the lowest. It is placed in a good location inside the device away from interference.

(3) Wynd Halo’s proprietary PM sensor seems to be the worst. Very bad PM2.5 and PM10 correlations. The log file kept registering 1μg/μ3 for PM1.0.

Air ID

The Air ID feature came with the version 2.1.02 of the iOS app (currently v2.1.03). Supposedly, Air ID combines raw sensor data with contextual data from the cloud and tells you if the air has pollen, forest fire smoke, or smog from the nearby industrial plant. Unfortunately, it was again a disappointment. I saw some inconsistencies and the information it provides you with is simple and frankly some areas don’t support the feature. An Air ID that I got followed the following logic: If VOCs are present, it tells you Poor Ventilation. Nothing contextual in my opinion.

Although air quality is good in their scale, I get a poor ventilation


I have tried to contact the company and ask them to comment about the results, unfortunately they don’t seem to care. The idea behind the technology is great, however, I do believe that you cannot create an amazing product by selling it that cheap. US$149 is cheap especially when you need to invest in R&D for a sensor. Maybe in the future they will be able to pull it through.


6 thoughts on “In-Depth Review: Wynd Halo 1st Edition Sensors

  1. Is it possible that the Wynd is actually accurate and all of the others are off by the same amount because of a common faulty assumption or implementation? E.G., if blue laser is indeed more accurate than red then could all PM’s using red be inaccurate in the same way by a similar amount?

    Liked by 1 person

    • It is a possibility but I doubt. I do believe a blue laser light is a cool idea but I feel the firmware and the algorithms don’t interpret data well. As I said in the post maybe in the future they will be able to pull it through. There is a lot of science behind even about the angle the laser light hits the particles, etc.

      Liked by 1 person

  2. We’ve had a Halo since the beginning of 2022. At first, the readings seemed OK, then CO2 went into the weeds. Did the rest, calibration, no help. Purchased a $60 CO2 meter that uses NDIR which I’m told is the most accurate kind of device. It doesn’t correlate with the Halo well at all. When C02 on the newer device is like 450, the Halo is over 1000! We plan to contact Wynd and see if they will replace the unit. But at this point, I have zero faith in the accuracy of the C02 and VOC meters.


    • Hi, thanks for your comment.
      Your point is correct. The Halo doesn’t have a dedicated CO2 sensor instead it makes an estimation based on the VOC values. As a result, you will never get the same values as a monitor with a CO2 NDIR sensor.

      Liked by 1 person

  3. Thanks for the fast reply. I do trust the NDIR unit, I’m just shocked that the difference between it and Halo is so far off. What’s odd is, sometimes they are close, within a dozen or less values, always when the air quality is lower towards the 400 limit, windows open etc. We close up and turn on the ERV, the Halo gets worse and worse until it’s like 800-1000 PPM higher than the HDIR. So weird. We don’t trust it at all after going thorugh a huge rabbit hole thanks to Halo, where we had the ERV tech’s come out and confirm it was working fine, duct cleaning (never hurts) etc. I’m going send a long letter to Wynd tech support and at least try for a replacement because again, early on, it wasn’t too bad. Glad I found your review, few and far between out there discussing this VOC issue. Thanks!

    Liked by 1 person

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