Detect breath

Using Arduino Sensors
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Hello,

I want to create a project in which arduino would detect when a human (or anything else) would breath into a sensor. I want it to be even a light breath. It has to be breath (CO2) no other gas. I want it to be accurate therefore no microphone. I found some really expensive co2 sensors on ebay for (50-60) USD. I belive there must be something cheaper to do this simple job. For example, do the alcohol detectors for few bucks detect sober humans breath? If not, what else could I use? I want it to be maximum abou 15 dollars. Thank you.

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CO2 detectors are relative expensive, 50-60$ are in fact cheaper ones

Breath also has a lot of water vapour so you could make a detector with a small mirror, a led and a sensor to measure the reflection.

Another option might be using a DHT11 (~10$) to detect humidity and temperature.
Air inhaled has different properties than air exhaled.
The DHT11 is not very good in humidity but good enough to see the difference

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there is this article from mit ,

rfcapture.csail.mit.edu

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A harmonica makes a noise when it detects breath....

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Humidity is probably a good way, it doesn't normally jump by 10's of percent in seconds so a breath is
going to be a pretty obvious signal I expect.

Of course temperature will also show a very strong signature unless its already ~37C.

The combination of temperature and humidity is probably even better.

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To reply your other question: breathalisers won't work, as they have sensors that detect ethanol, not carbon dioxide. Very different molecules.

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