Air quality monitors, decoded.
Your home's air changes all day. You just can't see it.
Modern UK homes are built and upgraded to keep heat in. That's good for energy bills, but it also means stale air, moisture and cooking fumes can linger when rooms aren't ventilated.
An air quality monitor turns the invisible into numbers you can act on: when to open a window, when to run the extractor fan, and when everything's fine as it is. The tricky part is that "air quality monitor" covers very different devices, and the box doesn't always make clear what's really being measured.
We've done the homework, so you don't have to.
The honest guide to air quality sensors.
Every monitor is only as good as the sensors inside it. Here's what each one does, and where its limits are.
NDIR CO₂
Uses infrared light to measure carbon dioxide directly, in parts per million (ppm). The clearest guide to whether a room needs fresh air.
Limits: doesn't detect particles, fumes, or carbon monoxide.
eCO₂ (estimated CO₂)
Found in some lower-cost monitors. It doesn't measure CO₂ at all: it estimates a figure from a gas (VOC) sensor.
Limits: readings can drift or jump with sprays and cooking, so they're less reliable as a ventilation guide.
PM2.5 & PM10 particles
A laser counts tiny airborne particles, such as smoke from cooking, candles, wood burners, and outdoor pollution drifting indoors.
Limits: tells you nothing about CO₂ or gases.
TVOC (gases and fumes)
Reacts to volatile organic compounds from things like paint, cleaning products, air fresheners, and new furniture.
Limits: shows a combined total rather than identifying any one gas, so it's best for spotting changes.
Temperature & humidity
Shows how warm and how damp a room is. Humidity is the number to watch if you're dealing with condensation on windows.
Limits: says nothing about stale air or pollutants on its own.
Formaldehyde (HCHO)
A specific gas that can be given off by some furniture, flooring, and building materials, especially when they're new.
Limits: low-cost formaldehyde sensors vary widely in accuracy.
Carbon monoxide (CO)
A different gas from CO₂. It's a job for a certified carbon monoxide alarm (EN 50291), not an air quality monitor.
Important: no air quality monitor should be used in place of a CO alarm.
Radon
A natural radioactive gas that's more common in some parts of the UK. Levels vary over time, so it's checked with dedicated long-term tests.
Limits: everyday air quality monitors don't measure it.
The sensor question, finally answered.
Start with what you want to know, then find the sensor that answers it.
| What you want to know | NDIR CO₂Core CO₂ and Core Max | PM2.5 particlesCore Max | TVOC / eCO₂TVOC in Core Max | Temperature & humidityCore CO₂ and Core Max | Certified CO alarm |
|---|---|---|---|---|---|
| Is this room stuffy and due some fresh air? | |||||
| What's the real CO₂ level, in ppm? | |||||
| Smoke from cooking, candles, or a wood burner | |||||
| Fumes from paint, cleaning products, or air fresheners | |||||
| Condensation and damp | |||||
| Is the room a comfortable temperature? | |||||
| Carbon monoxide from a boiler, gas fire, or stove |
eCO₂ sensors estimate CO₂ from other gases rather than measuring it, so they aren't counted for the CO₂ questions. Atmosense Core CO₂ includes NDIR CO₂, temperature, and humidity. Atmosense Core Max includes all the highlighted sensors (TVOC, not eCO₂).
What your CO₂ reading is telling you.
CO₂ rises as people use a closed room, so it's a simple way to see how well that room is being ventilated. As a rough guide:
- 400–450 ppmTypical fresh outdoor air.
- Under 800 ppmA well-ventilated room.
- Above 1,000 ppmThe room would benefit from more fresh air.
- 1,500 ppmAtmosense Core CO₂ sounds its built-in alarm as a reminder to ventilate.
These are general ventilation guides, not safety limits.
Six things worth checking before you buy.
- A real CO₂ sensor: look for "NDIR" in the specifications, not "eCO₂".
- A screen you can read at a glance: so you don't need your phone to check the room.
- Phone alerts: a notification when CO₂ reaches a level you choose, even when you're in another room.
- History graphs: trends over days and weeks show which rooms, and which times, need attention.
- A published accuracy figure: for example, ±(50 ppm + 5% of reading) for CO₂.
- Wi-Fi that suits your router: many smart monitors use 2.4GHz Wi-Fi, which most home routers support.
Common questions.
Is a CO₂ monitor the same as a carbon monoxide alarm?
No. Carbon dioxide (CO₂) and carbon monoxide (CO) are different gases. A CO₂ monitor helps you understand ventilation; it does not detect carbon monoxide and must never be used in place of a certified CO alarm (EN 50291).
Do I need a monitor that measures everything?
Not necessarily. If your main question is "when should I open a window?", an NDIR CO₂ monitor with temperature and humidity, such as Atmosense Core CO₂, covers it. If you also want to track smoke or fumes, Atmosense Core Max adds particle, TVOC, and formaldehyde sensors.
Where should I put an air quality monitor?
Choose an open spot at around desk or bedside height that represents the room. Keep it away from windows, doors, vents, radiators, heaters, and direct sunlight, and not right next to where you breathe, as this can briefly spike the CO₂ reading.
How many monitors do I need?
A monitor reads the room it's in. Most people start with the room they spend the longest in, such as the bedroom or home office, and add more if they want to compare rooms.
What does ppm mean?
Parts per million. A reading of 1,000 ppm means that, out of every million parts of air, 1,000 are carbon dioxide.
Start with the air you breathe most.
Atmosense Core CO₂ gives you NDIR CO₂, temperature, and humidity readings. Atmosense Core Max adds particles, TVOC, and formaldehyde. Both have a clear display, with phone alerts and history in the app.
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