# What Does the Aranet4 Do?
#### A CO2 monitor that tells you when to air out your room!
Aranet4 HOME measures CO2, 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. Battery powered, cable free, 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. CO₂
concentration levels of 1400 ppm (parts per million) and up are unhealthy and can cause drowsiness and decrease
cognitive function by 50%. 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. By monitoring pressure, the Aranet4 can automatically compensate for these variations, delivering consistent, precise CO₂ values regardless of environmental conditions.
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