Best Air Quality and CO2 Monitors UK (2026): Sensors That Actually Work

What is the best air quality monitor in the UK?

For most homes, the most useful air quality monitor is a CO2 monitor with a true NDIR sensor (non-dispersive infrared, which measures CO2 directly), because CO2 tells you when a room needs more fresh air. Our top pick is the Aranet4 HOME, a battery CO2 monitor that runs for years and that independent testers rate highly. The best budget NDIR monitor is the Sonoff AirGuard CO2, and the best all-in-one is the Airthings View Plus, which adds particles and radon.

Be wary of cheap "6-in-1" monitors that claim to measure CO2, formaldehyde and VOCs for under £20. Many estimate CO2 from a VOC sensor rather than measuring it, and the formaldehyde readings on low-cost devices are rarely reliable.

Our picks at a glance

How we chose

We prioritised the sensor inside, not the number of readings on the box. We rewarded monitors that state an NDIR CO2 sensor, which is the type the Health and Safety Executive recommends, and laser (optical) particle sensors for PM2.5. We checked hands-on results from HouseFresh's tests where available and verified UK prices at the brand or a UK retailer in October 2026. "Strong" means a stated NDIR sensor plus independent testing; "moderate" means a credible sensor type with no independent test we could find.

What should an air quality monitor measure?

CO2 (carbon dioxide) is your best guide to ventilation. People breathe it out, so it builds up in closed rooms. HSE says levels consistently above 1,500 ppm in an occupied room indicate poor ventilation, and that about 1,000 ppm corresponds to roughly 10 litres of fresh air per second per person. HSE also stresses CO2 is a broad guide to ventilation, not a direct health limit. Aim to keep bedrooms and home offices below about 1,000 ppm where you can.

PM2.5 (fine particles) come from cooking, toast, candles, wood burners and outdoor pollution. Optical (laser) sensors are the practical choice for homes, though the UK Air Quality Expert Group notes their accuracy varies and high humidity can inflate readings, so kitchens and bathrooms are tricky places for them.

VOCs (volatile organic compounds) come from paint, cleaning products, air fresheners and new furniture. Home monitors show a "total VOC" or VOC index. The AQEG report says total VOC readings are rarely a well-defined absolute value and are best used for trends, not compared with health limits for specific chemicals. Treat a VOC spike as a prompt to open a window, not a diagnosis.

Formaldehyde is the one people often want to measure, but cheap sensors are weak. HouseFresh found only one device in its tests specifically measured formaldehyde (HCHO). If formaldehyde is a real concern, for example after a renovation, a lab-analysed passive sampler from a specialist is more reliable than a gadget.

Humidity matters too: high humidity drives condensation and mould. Most monitors include it.

Why NDIR matters for CO2

Many budget monitors show "eCO2" (estimated CO2), calculated from a VOC sensor. It rises and falls with cooking smells and cleaning sprays rather than with actual CO2 from breathing, so it can tell you a room is fine when it is stuffy, or the reverse. NDIR sensors measure CO2 directly by how much infrared light it absorbs. If a listing does not say NDIR (or name a known photoacoustic sensor such as Sensirion's SCD4x), assume it is estimating.

Our picks

Aranet4 HOME: best overall

The Aranet4 HOME uses a true NDIR CO2 sensor and runs for up to four years on two AA batteries, with an e-ink screen you can read at a glance. HouseFresh rates it the best portable monitor, and its size means you can check bedrooms, offices and classrooms. We verified £178.80 including VAT at GMCI UK.

Honest caveat: it measures CO2, temperature, humidity and pressure only, with no particle or VOC sensor.

Sonoff AirGuard CO2: best budget

The Sonoff AirGuard CO2 is the cheapest monitor we found from a UK retailer that states an NDIR sensor (accuracy ±50 ppm + 5%). It shows CO2 on an LCD and can alert you through Apple Home, Google Home, Alexa or Home Assistant.

Honest caveat: no independent accuracy test yet, it needs USB power and 2.4GHz Wi-Fi for the app, and it does not measure particles.

Airthings View Plus: best all-in-one

The View Plus combines an NDIR CO2 sensor, a laser particle sensor, radon, VOCs, humidity and pressure, which makes it the obvious choice in radon Affected Areas. HouseFresh picks it as its best radon-capable monitor.

Honest caveat: at £259 it is expensive, the VOC reading is relative, and for a formal radon result you still need a validated three-month test (see our radon guide).

Apollo AIR-1: best for Home Assistant users

The AIR-1 uses Sensirion's SEN55 module for PM1 to PM10, VOC and NOx, with a CO2 option, and runs locally with no cloud or subscription.

Honest caveat: it has no screen, needs your own USB-C power supply and a Home Assistant setup, and the maker notes a 2 to 6°C temperature offset.

Netatmo Smart Indoor Air Quality Monitor: also consider

Netatmo's monitor tracks CO2, humidity, temperature and noise with app history and modes for babies and asthma.

Honest caveat: the UK page does not state the CO2 sensor type, and there is no on-device screen or particle sensor.

Sonoff AirGuard PM2.5: also consider

The PM2.5 version is a cheap way to see particle spikes from cooking, candles or a wood burner.

Honest caveat: the sensor type and accuracy are not published; treat it as a trend indicator.

What to do when the numbers are high

• CO2 above 1,000 to 1,500 ppm: open a window or trickle vents, leave internal doors open at night, or run a mechanical extract fan. HSE says CO2 is a guide to ventilation, so fresh air is the fix.
• PM2.5 spikes: use the cooker hood on its highest setting and vent outdoors, avoid burning candles and incense, and consider a HEPA air purifier for persistent problems.
• VOC spikes: find the source (new furniture, paint, air fresheners, cleaning sprays) and ventilate during and after use.
• Humidity above 60%: dry clothes outdoors or in a vented dryer, use extractor fans, and see our damp and mould guide.

Bottom line

Buy a monitor for the job it does well. A true NDIR CO2 monitor, such as the Aranet4 HOME or the budget Sonoff AirGuard CO2, is the most useful single tool for checking ventilation at home. Add particle sensing if you cook a lot, burn wood or live near busy roads, and choose the Airthings View Plus if you also need radon. Skip cheap 6-in-1 gadgets that estimate CO2 and promise formaldehyde readings they cannot deliver.