Show HN: A subtly obvious e-paper room air monitor
5 comments
·November 18, 2025Animats
There are lots of commercial gadgets like that.
Most of the affordable CO2 meters are relative, not absolute. They set their 400 PPM level based on the lowest value they ever see. That's usually OK, but it's not good enough for places with permanent people occupancy, such as nursing homes. Absolute detectors with NIST calibration are available but around US$500.[1]
[1] https://www.forensicsdetectors.com/products/carbon-dioxide-d...
zucked
Cool project. I've done something similar using defunct crypto Awair AQI sensors tied into Home Assistant. They have an LED panel in the front that can show overall AQI or any of the pollutants they track: https://www.getawair.com/products/element
The sky is the limit as to what you can do with Home Assistant automations.
It's surprising how quickly a room with a closed door and one person can go from ~ambient CO2 levels to 1000ppm+.
ozim
I was looking for cheap co2 sensors that can be deployed on RPi but I guess they all feel expensive.
dafelst
Germans sure love their Lüften
null
In the cold season we tend to keep the windows closed. The air gets "stale": humidity often rises above 60 %, which can harm our wellbeing and promote mould. At the same time the CO₂ level in the air increases, which impacts our ability to concentrate.
So I built a room air monitor that stays unobtrusive as long as everything is in the green zone, but becomes deliberately noticeable once thresholds are exceeded. For my personal love of statistics I also visualise the measurements in a clear dashboard.