How much does the DIY CO₂ monitor cost to build?

About €15–20 total: an ESP32 DevKit is around €6 and a Sensirion SCD40 breakout around €10, plus four jumper wires. Commercial CO₂ monitors with a comparable NDIR-class sensor, like the Aranet4, cost €200+.

Do I need to install any software to flash the ESP32?

No. The firmware flashes straight from Chrome or Edge over Web Serial — plug the board into USB, click Connect, click Flash. You only need PlatformIO if you want to build the open-source firmware yourself.

Which CO₂ levels are good, and when should I open a window?

Following the German CO₂-Ampel convention: below 800 ppm is good (green), 800–1400 ppm means ventilate soon (amber), and above 1400 ppm means open a window now (red). Outdoor air is roughly 420 ppm.

Where does my measurement data go?

Nowhere. The sensor talks to the dashboard over your USB cable or your local network, and history is stored in your browser. There is no cloud account, no server, and no tracking.

Kann ich die CO₂-Ampel ohne Hardware ausprobieren?

Ja — das Dashboard hat einen eingebauten Simulator mit realistischen Klassenzimmer- und Büro-Kurven. Einfach die Demo öffnen, alles funktioniert ohne Gerät.

CO₂ Beacon — DIY ESP32 CO₂ Monitor, Flashed From Your Browser