Aranet
Aranet4 Home CO2 Monitor
- Bluetooth
Verified September 2026
The reference-grade NDIR CO2 monitor: years on two AA batteries, an always-on e-ink display, and a core Home Assistant integration reading it passively over Bluetooth (enable "Smart Home integrations" in the Aranet app first). At around £189 it costs roughly three times the SwitchBot Meter Pro CO2 on this site, and the gap is calibration pedigree: Aranet's NDIR sensor is rated to ±(30 ppm + 3% of reading), tighter than SwitchBot's ±(50 ppm + 5%), and is the sensor independent reviewers reach for to sanity-check cheaper monitors against. Buy this for a CO2 number you trust without question; SwitchBot trades accuracy for half the price.
In Home Assistant
| Control | Type | What it does |
|---|---|---|
| CO2 | Sensor (ppm) | NDIR-measured concentration — the primary reading this device is bought for. |
| Temperature | Sensor | Ambient temperature, read passively from the same BLE advertisement. |
| Humidity | Sensor (%) | Relative humidity, read passively from the same BLE advertisement. |
| Pressure | Sensor | Barometric pressure. |
| Battery | Sensor (%) | Battery percentage remaining across the device's ~2-year AA battery life. |
| Threshold status | Sensor | Device's own colour-coded air-quality status derived from CO2 level, matching the e-ink display. |
HA's native aranet integration is Bluetooth passive-listen only, and requires firmware with the app's Smart Home Integrations toggle enabled — skip that step and the device simply never puts live readings into its advertisement packets, so HA sees nothing to discover. It exposes all four measurements (CO2, temperature, humidity, pressure) plus battery, and a colour-coded threshold status entity matching the e-ink display. Because there's no active-connection fallback, a monitor placed more than a room away from the HA host's Bluetooth adapter reliably drops to unavailable — an ESPHome Bluetooth proxy positioned near the sensor fixes this far more reliably than trying to stretch native adapter range, and is the standard fix reported on the HA forums for exactly this device.
Specs
- power
- 2x AA, circa 2 years
- display
- E-ink, always on, 3-colour threshold indicator
- requires
- HA Bluetooth adapter or ESPHome Bluetooth proxy
- co2 range
- 0-9999 ppm
- dimensions
- 66.5 x 66.5 x 22.4 mm, approx. 72g with batteries
- sensor type
- CO2 (NDIR), temperature, humidity, pressure
- co2 accuracy
- ±(30 ppm + 3% of reading)
- measurement interval
- Adjustable: 1, 2, 5 or 10 minutes