Why you should trust us

Tim Heffernan has overseen Wirecutter's air quality coverage since 2015, spanning five separate tests of air purifiers. In addition to directly testing air quality monitors, Tim reported this guide by interviewing representatives from five manufacturers to gain a better understanding of how the devices take their measurements and what they can be used for. John Holecek, a lab scientist and former NOAA researcher who specializes in aerosol and particulate pollution, has also contributed his professional expertise to our work on air quality products since 2015.

Who should get this

Even if you've used an air purifier for years with full confidence that it's working effectively, you're still probably in the dark about what air quality conditions it's facing and when its performance is needed most. That's because very few air purifiers offer direct air quality readings. Some have built-in sensors that can measure the air quality and adjust the machine's settings to address problems. But they don't usually tell you how much (and what type of) pollution they're measuring, nor why they're adjusting.

An air quality monitor can help demystify this by giving you measurements of what's currently in the air in any given room in your home. Knowing what's in your air can provide you peace of mind, and it may reveal pollution patterns or sources and help you take mitigating steps. If you live near a highway, for example, your air quality may go down during rush hours, prompting you to adjust your air purifier or AC in anticipation. Some monitors can offer you simple tips and advice for how to improve your air. It's possible to program a connected monitor to turn on a smart air purifier or central AC in the event of poor air quality.

But most of the time, any action you'd take based on an air quality monitor's reading are things you should do anyway. Open your windows on nice days—that'll help flush away volatile organic compounds (VOCs, or, more simply, gases and odors). If a monitor confirms your concerns about particulate pollution (such as from smoke, pollen, and mold), you'll need to keep an air purifier running. Air quality monitors can augment, but not replace, active air quality management.

We debated how necessary air quality monitors were when researching this guide, and in the end we came to see the appeal of having more information. That alone can make them a helpful companion to your other filtration equipment—if for no other reason than to confirm that there's nothing to worry about.

How we picked

To better understand how home air quality monitors work, who uses them, and what they can (and can't) do, we spoke with five companies that make them: Dylos, Kaiterra, Awair, Airthings, and Temtop. At the same time, we did a thorough search of the available models and began narrowing down our selections for testing.

We insisted that all of our selections be capable of measuring one specific form of air pollution: particulate matter of 2.5 microns or smaller, better known simply as PM2.5. We favored those that also measured volatile organic compounds, better known as VOCs (in practice, gases and odors). PM2.5 is of special concern because these particles can deeply penetrate the lungs and are known to cause health problems. VOCs include a huge range of compounds, the most well known of which is probably formaldehyde. A precursor chemical used in many glues, foams, plastics, and building materials found in homes, it is a known carcinogen.

Many air quality monitors also measure humidity, and some measure CO2, but these are not of particular concern to health, so we didn't prioritize them. Note: CO2 (carbon dioxide), the byproduct of respiration, is very different in its biological effects from CO (carbon monoxide), a byproduct of the combustion of hydrocarbons, such as gas stoves and gas or oil boilers. CO (but not CO2) can rapidly accumulate in a poorly ventilated home, and it is deadly. That's why most states require CO (carbon monoxide) monitors, like the ones we recommend in our guide to basic smoke detectors. These air quality monitors do not measure CO.

For Wi-Fi–enabled monitors, we looked for ones that had the ability to identify and offer air quality index (AQI) readings from a nearby outdoor weather station—typically run by local, state, or federal agencies—based on the monitor's location. These official AQI readings give you a measure of local outdoor conditions, so you can compare your indoor air, and also plan for any outdoor concerns. And we gave extra points to monitors that let you set multiple outdoor weather stations as references—for example, one near your home and one near your workplace. This is not to be confused with home weather stations, which usually don't measure AQI. And, bigger picture, there are many weather apps that can give you local AQI readings, so Wi-Fi connectivity isn't a must for air quality monitors.

The air quality monitor is primarily a device to convey information, so we looked for models that displayed their readings clearly, both on the device itself and, where applicable, in the app. We wanted clear information that required a minimum of interpretation or analysis. After all, you can't take action on your air quality (say, by turning on a purifier) if you can't easily read what your monitor is telling you.

Factors such as the number and quality of owner reviews, manufacturer history, and, to a lesser extent, price helped us narrow our selections further. Additionally, we came to realize that home air quality monitors come in two basic "flavors," handheld and desktop, and we made sure to include both on our list. Since desktop models are designed to live in the room with you and be on display all the time, we placed some emphasis on their size and aesthetic appeal. For handheld models, we sought ease of use, portability, and clear information.

We did not look at "personal air quality monitors," a new class of devices that are designed to be carried on a keychain or necklace to measure the air wherever you go. Based on common owner complaints—bad apps, connectivity issues, poor customer service—we don't think they're worth considering. Besides, we don't see a ton of utility in knowing what's in the air when you're out and about: Short of donning a respirator mask, there's nothing you can do to improve any problematic air you may encounter.

We wound up with seven models to test, drawn from a finalist list of about 20.

How we tested

We used the same room to test air quality monitors that we used to test air purifiers: a 135-square-foot conference room at Wirecutter's New York City office. We sealed the HVAC vents with tape and foil, to minimize their effect on the air quality. Then we set up the seven test models in one corner of the room, burned five matches in the other corner, and monitored the machines' responses to and measurement of the resulting cloud of smoke. We did this three times, clearing the air between tests with a Blueair Blue Pure 211+ air purifier.

We looked for consistency of readings among machines and noted any that seemed wildly out of the norm. We could not confirm their accuracy directly because all but one monitor in our test reported an algorithm-based estimate of the mass of particulates in the air, and our particle counter (a TSI Aerotrak 9306) reported a direct count of the number of particles. But we could judge whether the monitors were behaving as they should. After five years of testing air purifiers with this same type of particle counter, including a recent round of testing in the same room under the same conditions, we knew how the air quality would change over the course of the air quality monitor test. And we knew that any monitors that gave wildly off readings would therefore stand out.

We gave a great deal of attention to the monitors' interfaces, both on the machines and in their apps. On the physical monitors, we looked for simple controls and a clear display. In the apps, we first looked for easy installation and painless pairing with the monitors. During tests, we watched for both accuracy and response time, noting how quickly the monitors reacted to changing conditions. We then ran the apps for a week, noting any issues with app crashes, loss of pairing, or other annoyances. We also used this time to adjust the settings, changing, for example, the local outdoor weather stations informing the nearby air quality readings.

Our pick: Kaiterra Laser Egg+ Chemical

Photo: Michael Murtaugh

The Kaiterra Laser Egg+Chemical is the best air quality monitor for most people. With a clean design, simple and efficient physical controls and app, and smart functionality, it's the most versatile and capable of all the monitors we tested. It measures both particulates (PM2.5) and VOCs, and and uses local weather stations to report outdoor air quality. It was the easiest of our test machines to set up and to pair with its app (we used the Android version, on a Pixel 3a). The app itself was the best we tested: stable, logically laid out, and with air quality readings clearly displayed. And the monitor, which is about the size of a baseball and designed to sit on a desk or table, is equally easy to use. A single button cycles through the device's readings; the screen is bright and the display of information is simple; and at night, the screen can be shut off so it won't disturb your sleep. Finally, the Kaiterra is Apple HomeKit and IFTTT compatible (with Google Home and Alexa compatibility due by the end of 2019), and so the device can be used to control an air purifier or HVAC system to help manage your home's air quality.

The Kaiterra's app displays both current and historic air quality readings data in a clear, easy-to-read format. Photo: Michael Murtaugh

In our smoke test, the Kaiterra—along with the rest of our test units—began to register the change in air quality within seconds of the matches being lit. We were encouraged by this sensitivity: It means the Kaiterra is giving real-time readings, not delaying them. We also were encouraged by the consistency of the Kaiterra's readings. They tracked closely with those of three other monitors, suggesting, if not proving, that the readings were accurate.

Among the app-enabled monitors we tested, we found the Kaiterra to be the easiest to set up, customize, and navigate. Pairing the device to the app (Android version, on a Pixel 3a) was straightforward: The device easily connected to our office's Wi-Fi network, and pairing it to the app was almost automatic. We had more difficulties setting up some other Wi-Fi models, like the Awair 2nd edition.

The Kaiterra's app interface is both dead simple and rich in information. It displays the device's current indoor air quality index, the outdoor air quality index as measured by a nearby weather station, and charts of the last 20 hours' readings for both. Clicking on either chart opens a short menu that lets you display only specific readings (like PM2.5 and VOC) and adjust the chart's timeframe of readings (minutes to hours to days). Color codes (green, yellow, and red) indicate whether the readings represent good, moderate, or severely polluted air. And you can download all of this data should you choose to keep records.

The Kaiterra app also makes it easy to customize your device. A Settings page lets you add new weather stations (like one near home and another near work), additional devices (if you have multiple Eggs), and additional rooms (if, for example, you want to use the same device to monitor and record the air quality history of the living room during the day and the bedroom at night). The Settings page also lets you toggle between Fahrenheit and Celsius and the eight different display languages available.

The Kaiterra app proved extremely stable, never stopping on its own or losing its Wi-Fi connection in a week of testing.

Several competitors' apps offer similar richness of data and customization, but we found setting them up and navigating through their features to be more difficult. We ran into problems, including refusal to join a network, repeated app crashes, and clunky keyboard inputs. No other apps worked as simply or reliably as the Kaiterra's.

Finally, the Kaiterra device—the physical unit that measures your air quality, designed to live on a table or desk and display readings without using the app—had a level of simplicity that made it our joint-favorite (the other being the even simpler Temtop M10). It has a power button to turn it on and off, and a toggle button to jump between a handful of screens: local air quality index, indoor PM2.5 readings, indoor VOC readings, and display on/off. It's compact enough to live almost anywhere, and its three-hour battery life (similar to other monitors we tested) allows you to move it room to room to take spot measurements. The display on/off is an especially nice touch: It lets you shut off the rather bright screen when you go to bed, while the device continues to monitor the air.

Flaws but not dealbreakers

Our Kaiterra device initially and automatically connected to a nearby weather station (at Public School 19 in Queens, New York) that had not updated since December 2017. The Settings page of the app made it easy to connect to a functioning nearby station, but you should be aware that the automatic connection may not be accurate.

We wish the Kaiterra's device display gave readings in a larger, higher-contrast font, so you could read the display from across the room. The small, thin font the Kaiterra uses, against a white background, is hard to read except when you're up close.

The Kaiterra is compatible only with 2.4 G Wi-Fi, not 5G (the same is true of the other Wi-Fi–enabled devices we tested). If your home network is 5G only, it will still display readings on the device but will not connect to the app.

The Kaiterra Laser Egg+ Chemical is relatively new to the US market and has few Amazon reviews. Several reviews question whether the readings are accurate, and it's true that there's no way to independently confirm this device's accuracy (the way that you can, say, check your oven's accuracy by installing a separate thermometer). Based on our experience in testing, we have no reason to doubt the Kaiterra's accuracy.

Several other reviews mention having trouble connecting or staying connected to the app; these reviews are from early 2019, and when we tested in September and October, we found the app notably stable and simple to set up.

Also great: Temtop M10

Photo: Michael Murtaugh

If you don't need smart functionality or an app—if you just want to be able to glance at your air quality monitor and know what's going on in your air—we recommend the Temtop M10. It measures PM2.5, VOC, and formaldehyde (HCHO), and it gave virtually identical readings to the Kaiterra in our testing, confirming its accuracy. Its bright display can be read from across a room, and its tiny size and simple form fit nicely on a desk or bedside table. Lacking Wi-Fi connectivity, it has no associated app, let alone smart functionality. But for some people, that will work just fine—and the M10 usually costs less than the Kaiterra.

In our smoke test, the M10 gave almost the exact same readings as the Kaiterra, which matched our experience when testing air purifiers under the same conditions. This consistency gave us confidence in the M10's accuracy as well. It also shares with the Kaiterra a simple, intuitive interface: A single button turns the device on, and additional clicks cycle you through the M10's readings (PM2.5, VOC, formaldehyde, and indoor air quality index). If your air quality is bad, the readings turn from white to bright blue, and a small LED atop the device turns from green to red, alerting you to the problem.

And that is all the M10 does. With no Wi-Fi connectivity and no app, it doesn't track the readings over time; it doesn't offer outdoor air quality data from nearby weather stations; it doesn't give you suggestions for how to improve your air quality; and, of course, it doesn't let you check your air quality on your phone. If that sounds like blessed simplicity, you'll probably like it.

Like the Kaiterra, the M10 has few Amazon reviews yet. A few of the negative reviews question its accuracy, but again, there's no way for the average owner to independently test this. Based on our testing and experience, we have no reason to doubt its accuracy.

The competition

The Temtop M10 comes in two additional, similar versions. The P10 measures only PM2.5, not VOC, limiting its utility. But if particulates are your only concern, the P10 is significantly less expensive. The M10i, which we tested, is functionally identical to the M10, but it adds Wi-Fi connectivity and a simple app that displays the device's readings, tracks them over time, and lets you turn the device on and off. We think the Kaiterra Laser Egg+ Chemical offers a better in-app experience—and the Kaiterra is smart-home compatible, which the M10i isn't.

The Awair 2nd Edition is a beautiful-looking device, but we found it frustrating to use. It initially refused to connect with our office Wi-Fi. And after we finally got the device to connect, it—and it alone—kept losing the signal, forcing a manual reset. The app routinely crashed, as well. Finally, the hyper-minimalist aesthetic of the device is a hindrance in practice: Since the Awair has only an unlabeled bar chart to indicate readings, you're left to guess what the readings actually represent.

The IQAir Airvisual Pro easily connected to our Wi-Fi. Its app is clearly laid out, and both the app and the device offer simple, practical advice on how to address indoor air quality issues (for example, open a window if the outdoor air quality is good). But the device's physical interface is a clunky, frustrating experience. And the machine is simply far too expensive. For $270, you should get more than PM2.5 and CO2 measurements (plus humidity and temperature, which aren't strictly air quality measurements). Put another way: For a lot less than $270, our picks offer a lot more functionality and value.

The Dylos DC1100 is a very simple, very accurate particle counter that measures down to 1 micron—all the other devices we tested go to only 2.5 micron (PM2.5). But it's really a specialist's device, generating reams of data but leaving the analysis up to the user. For the small subset of people who want raw data above anything else, it may be attractive. But for most people, our picks' simpler displays and easy-to-digest alerts will be much more useful.

The Igeress Indoor Air Quality Monitor is one of a number of similar, relatively inexpensive monitors that we ran into in our search. We tested it because it is reasonably popular; it delivered wildly different readings from all the other monitors, leading us to doubt its accuracy.

The Temtop LKC-1000S+ (and the similar, less fully featured LKC-1000S and LKC-1000E) are handheld monitors. The 1000S+ we tested was accurate and easy to set up and operate. But after testing both handhelds and desktops, we strongly believe desktops are the right choice for most homes. They're smaller, designed to fit into anyone's decor, and don't look like a Star Trek prop.

The Atmotube Pro is a personal air quality monitor, designed to be carried on a keychain or clipped to a bag. As noted in How we picked, we did not test personal monitors in this guide.

The Plume Labs Flow, like the Atmotube Pro, is a personal air quality monitor, and we did not test them for this guide.

The Yvelines Indoor Air Quality Monitor is a carbon copy of the Igeress, which delivered dubious results in our testing.

The Awair Glow is a smart plug that gives a measure of indoor air quality based on VOC, temperature, and humidity readings, but it does not measure particulates, a requirement for inclusion in our testing.

Airthings is a well-regarded, Norway-based manufacturer of air quality monitors, specializing in radon detection. But none of their many devices measures particulates, a requirement for inclusion in our tests.

The Eve Room does not measure particulates, a requirement for our testing.

This guide may have been updated by Wirecutter. To see the current recommendation, please go here.

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