In coal mines the miners have traditionally used canaries to monitor the level of CO2. When the canary dies the miners get ready to leave.
But there are more sophisticated instruments for CO2 detection. The “Testo Model 535 Carbon Dioxide Monitor” is a hand-held monitor which detects levels from 0 to 9999 ppm and has a dual probe to measure airflow through both an incoming and out-going duct. It’s cost is about $730 U.S. Dollars.
Green houses use CO2 monitors in order to assure that plants are receiving enough CO2 to carry on photosynthesis. Often these monitors are built to trigger a CO2 enrichment device when levels drop below that which is optimal for plant growth. However Green Air Products does produce a “Portable Carbon Dioxide Monitor Model CDM-7001″ which is hand held and would be well suited for a variety of applications. It also gives a temperature reading and is able to register a CO2 level within 30 seconds. It has a data port that can output data to a windows based application.
This monitor operates 70 hours on 4 AA batteries. The cost is about $925 US dollars. GE Telaire makes a device that looks identical in every aspect and sells for about $425."
They are on the way. "Internal combustion" is not a real gud idea.
Indoor combustion heats hundreds of thousands of home in the US. Ventless indoor combustion is another issue. Oxygen depletion will like be the first problem, which is why O2 sensor are far more commonly recommended.