The Most Popular CO2 Monitor, Reviewed
The Aranet4 has become the go-to CO2 monitor recommended by indoor air quality advocates, scientists, and health-conscious consumers worldwide. But does it live up to the hype? We put it through thorough real-world testing.
Design and Build
The Aranet4 is refreshingly simple. It features a 2.9-inch e-ink display that shows CO2 (ppm), temperature, humidity, and atmospheric pressure. The e-ink technology means it is easy to read in any lighting, including direct sunlight. At just 100 grams and roughly the size of a deck of cards, it is genuinely pocket-portable.
The back has a small stand and a magnetic mount, so it sits on a desk or sticks to a fridge effortlessly.
Sensor Performance
The Aranet4 uses an NDIR sensor manufactured by Sensirion. In our testing against calibration reference instruments:
- Accuracy: Consistently within +/- 30 ppm at typical indoor levels (400-2,000 ppm)
- Response time: Roughly 2 minutes to reflect a change in environment
- Measurement interval: Every 1, 2, 5, or 10 minutes (configurable via app)
- Calibration: Supports both ABC and manual calibration. See our calibration guide.
Battery Life
This is where the Aranet4 truly shines. Running on two AA batteries, it lasts approximately two years at the default 2-minute measurement interval. No charging cables, no forgetting to plug it in — it simply works.
App and Connectivity
The Aranet4 connects via Bluetooth to a well-designed mobile app (iOS and Android). The app displays:
- Real-time readings with colour coding
- Historical data graphs (up to several weeks stored on device)
- Configurable alert thresholds
It also integrates with Home Assistant for smart home automations, though it lacks native WiFi — a deliberate trade-off for battery life.
What It Lacks
- No WiFi — you must be within Bluetooth range to sync data
- No PM2.5 or VOC sensors — it measures only CO2, temperature, humidity, and pressure
- Price — at roughly $200-250, it is not the cheapest option
Verdict
The Aranet4 earns its reputation. For accuracy, battery life, portability, and simplicity, it is the best all-round CO2 monitor available. If you need PM2.5 or VOC monitoring, pair it with a complementary device — see our best home monitors guide. For a brand comparison, read our Airthings vs Aranet analysis. Estimate your monitoring needs with the CO2 calculator.