> For the complete documentation index, see [llms.txt](https://help.aranet.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.aranet.com/aranet4/aranet4-home/general/about-aranet4.md).

# About Aranet4

#### A CO<sub>2</sub> monitor that tells you when to air out your room!

Aranet4 Home measures CO<sub>2</sub>, temperature, humidity, and ambient pressure in real time. It shows when indoor air becomes stale and reminds you to ventilate for better focus, sleep, and health. The sensor is battery-powered, cable-free, and it connects to the Aranet Home app for trends and alerts.

The device is suitable for monitoring the CO₂ level at home, in school, office, or any other indoor environment.

Measurement data is displayed on a power-efficient e-ink screen with a long battery life. Additionally, the device provides visual and optional buzzer notifications when the CO₂ concentration becomes unhealthy.

{% hint style="info" %}
CO₂ concentration levels of 1400 ppm (parts per million) and up are unhealthy and can cause drowsiness and decrease cognitive function by 50%.
{% endhint %}

A high concentration of CO₂ is an indicator of insufficient ventilation, which can increase the risk of infection with airborne diseases.

#### Carbon Dioxide (CO₂)

The Aranet4 uses a Non-Dispersive Infrared (NDIR) sensor to measure carbon dioxide levels. Inside the device, an infrared light source shines through an air chamber toward a detector.

* CO₂ molecules absorb light at a specific infrared wavelength (\~4.26 μm). By measuring how much light is absorbed, the device calculates the CO₂ concentration.
* NDIR sensors are highly stable, selective, and the industry standard for accurate indoor air monitoring.

#### Temperature and Relative Humidity (T/RH)

Temperature and humidity are measured using a precision digital sensor that includes a tiny thermistor and a capacitive humidity element.

* The thermistor changes its electrical resistance with temperature, while the humidity element changes capacitance based on moisture in the air.
* The sensor converts these physical changes into digital readings, giving accurate T/RH measurements with minimal drift.

#### Atmospheric Pressure (hPa)

The Aranet4 includes a barometric pressure sensor to ensure accurate CO₂ measurements. Because NDIR CO₂ sensing depends on the number of gas molecules inside the optical chamber, changes in atmospheric pressure — caused by weather or altitude — would otherwise influence the reading.

{% hint style="info" %}
By monitoring pressure, the Aranet4 can automatically compensate for these variations, delivering consistent, precise CO₂ values regardless of environmental conditions.
{% endhint %}

#### Screen indications

Besides the measurements, the Aranet4 screen can show these indications:

| Indication              | Meaning                                                                                                                           |
| ----------------------- | --------------------------------------------------------------------------------------------------------------------------------- |
| Inverted screen         | The CO₂ level has reached the red threshold. Ventilate the room.                                                                  |
| Calibration progress    | A CO₂ calibration is running. See [Calibration & Errors](/aranet4/aranet4-home/usage-and-measurements/calibration-and-errors.md). |
| Six-digit PIN code      | The device is ready to pair. Enter this code in the Aranet Home app.                                                              |
| Do not remove batteries | A firmware update is running. Do not remove the batteries until it is finished.                                                   |
| Empty batteries         | The batteries are empty. Replace them.                                                                                            |


---

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