# SONOFF AirGuard CO2 Monitor, Matter Compatible, NDIR Sensor

Source: https://www.ranked10.co.uk/home/best-air-quality-monitor/sonoff-airguard-co2
Ranked #5 in "Best Air Quality Monitor 2026: Fewer Numbers, Better Sensors": https://www.ranked10.co.uk/home/best-air-quality-monitor

- Price: £42.77 (checked on Amazon UK on 2026-09-11)
- Amazon rating: 4.2 from 166 ratings
- Buy on Amazon: https://www.amazon.co.uk/dp/B0G2WDPB29?tag=ranked10-21

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.

## Specification

| Field | Value |
|---|---|
| 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 |

## 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.