How a DIY maker fixed a dangerous flaw in CO₂ monitors

Maker William Collis discovered a critical flaw in his home CO₂ monitoring setup: when the sensors failed, the system would continue displaying the last known-good reading, creating a dangerous illusion of safety. His custom-built monitors, using Sensirion SCD30 sensors paired with Seeed XIAO ESP32-C3 boards running ESPHome, were silently giving him a false sense of security.

To solve this, Collis modified the system so that a sensor failure triggers a visible fault indicator—a flashing LED—instead of hiding behind stale data. The fix, implemented entirely within the ESPHome configuration without firmware rewrites, provides a crucial safety upgrade for anyone monitoring indoor air quality. This project highlights that in safety-critical DIY systems, visible failure is as important as accurate measurement.