If people want a more flexible, less crazy expensive option, it's fairly straightforward to build a WiFi-connected sensor with an ESP32 devkit [0], an off-the-s

If people want a more flexible, less crazy expensive option, it's fairly straightforward to build a WiFi-connected sensor with an ESP32 devkit [0], an off-the-shelf sensor like the SCD30 [1] and ESPHome [2]. This is simple to assemble, will give you fairly good, repeatable readings, auto-calibration that performs pretty well and an open-source platform with full access to your data rather than a proprietary cloud application. Full cost should be ~$70, I'd expect assembly and flashing to take ~1h the first time. The most complicated thing you'll have to do from an electronics standpoint is solder on the pin header to the sensor, other than that it's just jumper wires and flashing over USB. No need for adding resistors or capacitors or anything like that. If you're not comfortable with soldering, I _think_ the evaluation kit for the SCD30 [3] comes with pre-assembled headers. There's also a third-party variant [4] that comes with a cable header you can break out [5]. I strongly recommend that you use the SCD30. I've tested a variety of sensor components from a variety of manufacturers and the SCD30 was by far the best performing. Other sensors have problems with auto-calibration in a residential environment so either give nonsense readings or drift without periodic manual calibration. However if you want something _really_ cheap, you can replace the SCD30 with the ~$20 MH-Z19 and the total price will be ~$30. The auto-calibration on these is utterly terrible however, so you'll need to manually calibrate it with fresh air every couple of months to compensate for drift. And as others have warned, beware of retail products. A lot of them have fake "CO2" or "eCO2" sensors that don't measure CO2 but try to guess it based on other measurements. These are completely useless and are not at all indicative of actual CO2 levels. [0]: Purchase: https://octopart.com/esp32-devkitc-32d-espressif+systems-92405929 https://octopart.com/esp32-devkitc-32d-espressif+systems-924..., info: https://www.espressif.com/en/products/devkits/esp32-devkitc/overview https://www.espressif.com/en/products/devkits/esp32-devkitc/... [1]: Purchase: https://octopart.com/scd30-sensirion-89692236?r=sp https://octopart.com/scd30-sensirion-89692236?r=sp, info: https://www.sensirion.com/en/environmental-sensors/carbon-dioxide-sensors/carbon-dioxide-sensors-co2/ https://www.sensirion.com/en/environmental-sensors/carbon-di... [2]: https://esphome.io/ https://esphome.io/ [3]: https://octopart.com/sek-scd30-sensor-sensirion-101025983?r=sp https://octopart.com/sek-scd30-sensor-sensirion-101025983?r=... [4]: https://www.seeedstudio.com/Grove-CO2-Temperature-Humidity-Sensor-SCD30-p-2911.html https://www.seeedstudio.com/Grove-CO2-Temperature-Humidity-S... [5]: https://www.seeedstudio.com/Grove-4-pin-Female-Jumper-to-Grove-4-pin-Conversion-Cable-5-PCs-per-PAck.html https://www.seeedstudio.com/Grove-4-pin-Female-Jumper-to-Gro...