I’ve been working closely with the home automation community @ domoticaforum.eu to create a CO2 sensor for HVAC that connects easily with home automation systems - e.g. via MQTT or HTTP http://www.domoticaforum.eu/viewtopic.php?f=7&t=11007&start=15.
I thought you may be interested in this as well.
I am selling the current version at http://shop.vair-monitor.com/index.php?rt=product/product&product_id=124 (you can use coupon code: VTHINGS_5 for 5% discount).
As an upgrade, currently i am running an Indiegogo campaign for a sensor that:
- does not require fresh air for calibration (most others need it at least each few days)
- can communicate via 433 Mhz interface
If you need more information on this - i will be glad to answer