Indoor Air Quality Monitors

Your Complete Guide to Indoor Air Quality Monitors

Why use an indoor air quality monitor?

There are three main reasons to use an indoor air quality monitor:

1. They can literally save your life. (No big deal!) Indoor air quality monitors can detect radon, and alert you to high PM 2.5 levels.

• Radon is a colorless, odorless radioactive gas that's the leading cause of lung cancer in non-smokers. It seeps into your home through from the radon-containing bedrock under your foundation, and you have no way of knowing it's there without testing. An air quality monitor with radon detection gives you continuous readings so you can catch dangerous levels early and take action.

• PM 2.5 (Particulate Matter smaller than 2.5 microns) comes from every day cooking, wildfire smoke, and outdoor pollution that infiltrates your home. These tiny particles are so small they are able to travel deep into your lungs and enter your bloodstream. Because the blood takes them all throughout your body, PM 2.5 is linked with many kinds of diseases, including heart disease, stroke, lung cancer, and premature death. When you can see PM 2.5 levels spike on your monitor, you know exactly when to close windows, turn on your air purifier, or turn up your exhaust fan.

2. They can make your daily symptoms better. Indoor air quality monitors track indoor VOCs and CO2, as well as the humidity levels that contribute to a mold-friendly environment.

• VOCs (volatile organic compounds) are gases like formaldehyde and many, many others that are released from everyday items like cleaning products, air fresheners, new furniture, paint, and scented candles. They often smell, but not always, and if they accumulate in your indoor air, they can trigger headaches, dizziness, eye and throat irritation, and worsen asthma symptoms. Some VOCs are also linked to long-term health effects. Your monitor helps you identify which products or activities cause spikes, so you can ventilate, turn your air purifier on, and start to understand patterns.

• CO2 (carbon dioxide)builds up surprisingly fast in closed spaces—especially in your bedroom at night, in your home office during the day, and especially when a large group of people is all in the same room. While CO2 itself isn't toxic at typical indoor levels, concentrations above 1,000 ppm cause fatigue, difficulty concentrating, headaches, and that stuffy, drowsy feeling you get in poorly ventilated rooms. When you watch your monitor and see CO2 climbing, then crack a window and watch it drop, you'll immediately understand why you feel so much more alert and energized with proper ventilation.

• Humidity: mold grows best in humid environments. An indoor air quality monitor is an objective way to let you know if you’re over-doing it with a humidifier, or if your house tends toward more moisture, and you investing in a dehumidifier is a good idea. Preventing mold growth can reduce allergies, mold toxicity symptoms, and protect you and your home’s long-term health.

3. They take the guesswork out of air purification and ventilation, reduce energy costs (and arguments with your partner ;). Knowing when to turn up your air purifier or open a window—even when it's cold outside—is just as useful as knowing when your indoor air is healthy and you can relax.

• Without a monitor, there are lots of questions: Is your air purifier actually doing anything? Should you open windows during wildfire season? Is that new rug off-gassing chemicals? Is it smoky in my kitchen after cooking? An air quality monitor gives you objective data that answers these questions in real-time.

• An air quality monitor helps you make smart decisions about when ventilation is worth the energy cost, when to run your purifier on high, and—just as importantly—when your air is clean enough that you can stop worrying and simply enjoy your home.

• Reduces arguments with your partner, spouse, or roommate: I used to over-ventilate, leaving my house very fresh, but my husband very cold and our heating bill high. Now we can use our indoor air quality monitor as an objective measure— everyone is happier!

What pollutants do indoor air quality monitors measure?

Continuous, comprehensive Indoor Air Quality Monitors typically measure the four most common indoor air pollutants, as well as temperature and humidity, and radon:

• PM2.5 (Particulate Matter): includes fine particles from smoke, dust, and outdoor pollution that can penetrate deep into your lungs and bloodstream, contributing to heart disease and asthma.

• CO2 (Carbon dioxide): builds up in poorly ventilated spaces and causes headaches, fatigue, and reduced concentration—high levels also indicate your room isn't getting enough fresh air.

• VOCs (Volatile Organic Compounds): gases released from cleaning products, furniture, paints, and building materials that can trigger respiratory symptoms. This is measured as total VOCs (TVOCs)— home-use indoor air quality monitors cannot measure individual types of VOCs, like formaldehyde for example.

• Radon: the leading cause of lung cancer in non-smokers.

• Temperature

• Humidity: high humidity promotes mold growth

Some indoor air quality monitors are even broader:

• The Awair Omni tracks most of the data above, plus PM10 (large particle), sound levels in decibels, and light levels — but it’s generally only available for businesses.

Some air quality monitors are more focused:

• Radon Detectors measure radon only.

• Hygrometers measure humidity only.

• Carbon monoxide (CO) detectors measure carbon monoxide only.

• Non-continuous, point-in-time air quality testing can catpure a broad range of information, potentially measuring hundreds of types of VOCs, but the sample is focused on a short period of time. The air sample must be sent in and analyzed in a laboratory.

How accurate are indoor air quality monitors?

Air quality monitor accuracy varies wildly by brand, and low-cost home monitors are often very inaccurate. The most accurate multi-pollutant monitors typically score above 0.9 (very good!) on AQ-SPEC tests, but cost $1,000+. But, there are a handful of home models that come close and cost much, much less.

Indoor air quality monitors for your home operate on an invisible level, so it’s important to know they’re doing the job correctly and not giving you false readings. Look for the following:

• AQ-SPEC: This database compares low-cost air quality monitors for home to the super-accurate, super-expensive air quality monitors used by scientists, to see how closely their readings match. The scores range from 0 to 1.0. A score of 0 means they don’t agree at all. A score of 1.0 means they agree perfectly. A score of 0.5 means they agree about half of the time. Choosing an air quality monitor with a score as close to 1.0 is ideal. It’s interesting to see how inaccurate some of the models are! One of the cons of this list is that it hasn’t tested all available models, and most of the ones it has tested with good readings are still very expensive (like the Air Quality Egg), discontinued (Kaiterra Laser Egg), or difficult to set up and use in a home. I expect this will continue to change as the need for in-home air quality monitoring continues to rise.

• RESET certification: brands that offer commercial air quality monitors (for buildings, schools, etc) can have their monitors RESET certified, which is a third party approval that it the monitor is accurate. However, it is not usually a certification brands are willing to pay for and go through for residential home air quality monitors. Still, a company that has RESET certification for its commercial models is generally more trustworthy, and a good signal that they have good engineering practices and the skills to make accurate home monitors. Not perfect, but since we don’t have anything other than patchy AQ-SPEC testing, it’s a good stand in for now.

• C-NRPP approval: this is third party testing done in Canada for radon monitors, which again, doesn’t always apply to air quality monitors overall, which also measure CO2, VOCs, and PM2.5. But, like RESET certification, it is a good general “green flag.”

• AIRLAB Microsensors Challenge: this is a French organization that tests air quality monitors. Again, not comprehensive, but helpful! I suspect this will become more and more popular as air quality continues to gain attention for how important it is to our health.

What's the difference between a cheap air quality monitor and an expensive one?

The difference comes down to sensor quality and measurement accuracy. Cheap monitors (under $50) typically use basic infrared sensors that give you rough ballpark estimates—they might tell you air quality is "good" or "bad" but the actual numbers can be off by 50% or more. These budget monitors are better than nothing for general awareness, but you can't trust them for precise readings.

Mid-range monitors ($150-300) use laser particle counters and more sophisticated chemical sensors that provide much more accurate data—typically within 10-20% of laboratory-grade equipment. This accuracy matters when you're making decisions like "do I need to remediate for radon?" or "is my air purifier actually working?"

High-end monitors ($300-1,000) often include features like RESET certification (commercial-grade accuracy standards), longer sensor lifespans, and the ability to track multiple pollutants simultaneously with minimal drift over time. These are not always available for home use, or are cost prohibitive.

Do air quality monitors measure formaldehyde?

No, home-use indoor air quality monitors are not capable of distinguishing formaldehyde from other VOCs. While it is possible to measure formaldehyde using very advanced, expensive, laboratory-grade equipment, residential monitors claiming they can measure formaldehyde separately are overstating their abilities—and this is a red flag about the monitor's overall credibility.

You can see this for yourself in YouTube videos where people open a beer or peel an orange close to a "formaldehyde sensor," and the numbers go off the charts. This is a false reading. The sensor is simply detecting VOCs from the beer or citrus oils, not formaldehyde itself (which isn't present in beer or oranges). The monitor can't tell the difference.

Brands that skip this gimmick are more likely committed to providing you with accurate, honest data about your indoor air quality. (Sorry, Dyson.)

Can air quality monitors detect mold?

No, air quality monitors cannot directly detect mold spores or identify mold presence. However, they can alert you to conditions that promote mold growth—specifically high humidity levels above 60%. Mold thrives in humid environments, so if your monitor consistently shows humidity readings in the 60-80% range, you have a mold-friendly environment even if you don't see visible growth yet.

If you're concerned about existing mold, you'll need a professional mold inspection — I recommend finding a certified inspector through ACAC. These specialists are trained in legitimate mold testing and reasonable remediation methods— no gimmicks. Your air quality monitor is best used as an early-warning system to prevent mold problems before they start by helping you maintain optimal humidity levels (30-50%).

How long does it take for an air quality monitor to give accurate readings?

Most indoor air quality monitors provide initial readings within 1-3 minutes of being plugged in, but they need 24-48 hours to calibrate and give you truly accurate baseline data. The sensors need time to adjust to your specific indoor environment and stabilize their readings.

During this calibration period, you might see numbers fluctuate more than usual—this is normal. After the first few days, your monitor will provide more consistent, reliable data. For continuous radon monitors, you'll usually need at least 7 days of continuous monitoring to get a meaningful average.

Are the air quality sensors on air purifiers accurate?

Short answer: No, the built-in air quality sensors on most air purifiers only give you a loose approximation of your actual air quality, not precise readings you can trust. There are two main reasons why air purifier sensors aren't reliable:

1. Air purifier sensors use cheaper, less accurate technology. Making an accurate indoor air quality monitor is difficult and expensive—the most reliable standalone home monitors cost $100-600. Most air purifiers use basic infrared PM2.5 sensors that are inexpensive to manufacture but provide only rough estimates. It would significantly increase the cost of an air purifier to include a truly accurate sensor, so air purifier brands typically use budget components that give you a general idea rather than precise data.

2. Air purifier sensors measure the wrong location. The sensor is built into the air purifier itself, which means it's measuring the air quality immediately around the device—air that has just been cleaned. This doesn't reflect the actual air quality across the room where you're sitting, which is what you really need to know. The purifier might show "good" air quality while the air on the other side of your room remains polluted.

If you want accurate air quality readings, invest in a separate, dedicated indoor air quality monitor and place it away from your air purifier—ideally where you spend the most time. Use the purifier's built-in sensor as a rough guide, but rely on your standalone monitor for real data about whether your air purifier is actually improving the air you breathe.

This approach costs more upfront but gives you the objective information you need to know if your air purification strategy is actually working.

What's a good air quality score on my monitor?

Most smart monitors will color-code readings for you: green means good, yellow means moderate, red means poor. This can be really handy as a way to alert you to open the windows, but you’ll need to open your app or look deeper into the monitor’s interface to understand which pollutant is causing a problem. If it’s VOCs, opening a window is adequate. If it’s radon, that’s a more serious concern! (Read how to deal with radon on my radon page.)

If you’re interested in the details of what the colors mean, here are general guidelines for optimal levels you should aim for indoors:

• Radon: below 4.0pCi/L

• PM2.5: below 9g/m3

• VOCs: below 400ppm

• CO2: below 600ppm

• Humidity: 30-50%

These are based on RESET guidelines, which set standards for commercial building air, the EPA’s radon guidance, and the WHO (World Health Organization) guidelines for outdoor air. The EPA recommends PM2.5 should be below 9g/m3, but it’s interesting to note that the WHO is aiming to decrease the standard to 5g/m3 to decrease disease and death worldwide. I use these values because there isn’t an official set of residential indoor air guidelines yet.

A note: these levels are very hard to achieve in any given moment, so it’s important to use your monitor to get average values and understand patterns over time — days, months, and years. Notice what causes air quality to deteriorate and improve. For example, when I cook on the stove, my PM 2.5 skyrockets to over 200 sometimes (watch my video of this happening here), and when I do yoga inside, my CO2 easily jumps over 1,000 (see the video of this happening here). But, the levels drop quickly with proper ventilation, and my month-long and year-long averages are within guidelines.

In short, a continuous indoor air quality monitor is best for identifying patterns and averages for healthier home air over time.

Do I need an air quality monitor in every room?

No. Start with one monitor in the room where you spend the most time—typically your bedroom or main living space. Bedrooms are especially important because you spend 6-8 hours there with the door closed, allowing CO2 and VOCs to build up overnight.

If you can afford multiple monitors, prioritize these locations: your bedroom, your home office (if you work from home), and your basement (for radon detection, since it accumulates in lower levels). Kitchens benefit from monitoring too, but if budget is limited, a single well-placed monitor in your primary living space will give you the most valuable data about your home's overall air quality patterns. I personally have one in my office and one in my kitchen because after using one in my bedroom for months, I noticed the air quality stays consistently good (I constantly have my windows open and air purifier on!) Things change a lot more in my office and kitchen, so I need to adapt throughout the day.

How often do air quality monitor sensors need to be replaced?

This varies significantly by pollutant type and monitor brand. Most PM2.5 sensors last 3-5 years before accuracy degrades, while CO2 sensors can last 10+ years. VOC sensors typically need replacement every 2-3 years. Radon sensors in continuous monitors usually last 5-10 years.

Check your monitor's specifications for sensor lifespan, and watch for signs of inaccuracy like readings that seem stuck, sudden unexplained spikes, or results that don't match what you'd expect (like showing perfect air quality while you're cooking with smoke visible in the kitchen). Most monitors don't alert you when sensors need replacement, so you'll need to track this yourself.

Will an air quality monitor work during a power outage?

Airthings, Atmotube, Aranet, and Temtop will all stay on during a power outage, since they are all battery-powered.

Most plug-in air quality monitors stop working immediately during a power outage since they don't have battery backup. When power returns, they'll need to recalibrate (usually 1-24 hours depending on the model), and you'll lose all data from the outage period.

If continuous monitoring during outages is critical for you—for example, if you're tracking radon levels in an area with frequent power disruptions—look specifically for monitors that advertise battery backup or consider a battery-powered radon-only detector as a backup device.

Most monitors retain their historical data through power outages, so you won't lose your long-term trends, just the real-time readings during the outage itself.

Can I use an air quality monitor to test my car's air quality?

Yes, portable air quality monitors work in vehicles, but you'll need a model that's either battery-powered or can connect to a USB power source. This can be useful for understanding if your car's cabin air filter needs replacement or if you're being exposed to high pollution levels during your commute.

The Atmotube was specifically designed for this, but other models would need time to calibrate to the car’s conditions.

Car air quality changes dramatically based on whether you're using recirculated air versus fresh air intake, whether you're in traffic or on a highway, and whether your windows are open. For meaningful data, you'll want to monitor over multiple trips in similar conditions rather than relying on a single reading. PM2.5 and CO2 are the most relevant metrics for vehicle air quality.

Do air quality monitors emit radiation or are they safe to keep in bedrooms?

Indoor air quality monitors are safe to keep in bedrooms, including next to your bed. They do not emit any radiation—they're passive sensors that detect and measure pollutants in the air around them. The only thing they emit is a small amount of light from the display screen, which you can usually dim or turn off completely in settings.

The electrical components in an air quality monitor operate at very low power (similar to a nightlight or phone charger) and produce no meaningful electromagnetic fields. If you're concerned about the display light affecting your sleep, most models allow you to turn off the screen while still collecting data, or you can simply place the monitor a few feet away from your bed where the light won't bother you.