Rank #5 in Best Air Quality Monitor 2026: Fewer Numbers, Better Sensors
SONOFF AirGuard CO2 Monitor, Matter Compatible, NDIR Sensor
Price and rating as shown on Amazon when we collected them. Both change.
The SONOFF AirGuard is the cheapest monitor here that measures CO2 with a real NDIR sensor, at £42.77. It covers 400 to 5000ppm, updates every five seconds, alarms above a threshold you set, and connects to Apple Home, Alexa, Google Home and SmartThings through Matter.
Its best feature is a line in the specification table: the accuracy is given as ±(50ppm + 5%), an absolute plus percentage figure, which is how CO2 sensors are honestly specified. It is fifth because it measures only three things, has no battery, and carries a smaller sample — 166 ratings at 4.2 stars — than the monitors ranked above.
How those 166 ratings break down
An average hides its own shape. This is the spread behind the 4.2 stars.
Specification
Exactly as published on the Amazon listing, field for field.
| CO2 sensor | NDIR, 400 to 5000 ppm |
|---|---|
| Accuracy as listed | ±(50ppm + 5%) |
| Response | Updates every 5 seconds |
| Smart home | Matter, Apple Home, Alexa, Google, SmartThings |
| Power | Not battery powered |
| Ratings | 4.2 from 166 |
What buyers actually say
Quoted from customer reviews on Amazon
Verified purchase“Easy to use and it's doing what it promises.”
What it is up against
The rivals it was ranked against in Best Air Quality Monitor 2026: Fewer Numbers, Better Sensors.
Rank #1
Aranet4 Home Wireless Indoor Air Quality Sensor, NDIR CO2 Monitor
£189.00
Rank #2
Temtop M2000 2nd Air Quality Monitor, PM2.5 PM10 CO2 HCHO
£158.64
Rank #3
Temtop Air Quality Monitor LKC1000S+ 2nd, PM2.5 PM10 HCHO TVOC
£129.99
Rank #4
Airthings 2960 View Plus, Radon and Air Quality Monitor with PM2.5
£166.99
Questions people ask
Why is ±(50ppm + 5%) better than ±1 PPM?
Because it is true. CO2 sensors are less accurate near the bottom of their range, so an absolute plus percentage figure is how real performance is stated. A flat ±1 PPM claim is not achievable in a consumer device.
Does it need batteries?
No, which is also its limitation: the listing says continuous power and buyers confirm it needs a USB charger or a power bank.
What can it connect to?
Matter, Apple Home, Amazon Alexa, Google Home and SmartThings, plus the manufacturer app for history and alerts.
Does it measure particles?
No. It measures CO2, temperature and humidity. For PM2.5 you need one of the Temtop monitors on this page.
Is the alarm adjustable?
Yes, you set a CO2 threshold and the monitor sounds an alarm and shows a colour LED when it is crossed.
How many ratings does it have?
166 at the time of collection, averaging 4.2 stars, with 62 per cent five-star and 9 per cent one-star.
Comments
Reader comments are not checked against the manufacturer's claims above.
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