Somebody asked on G+ about sensing the breath that would blow out candles. I took up the challenge and figured I would try with a thermocouple, as the wire is cheap! A two junction system senses the difference in temperature between the two ends, requires no excitation voltage, but produces an output less than a millivolt, so major amplification is required.
This video shows the performance with the the thermocouple run through 2 AD 8221 instrumentation amps like I used for the load cells, each with gain set around 1000, so the output is saturating. The voltage will be low if the left junction is warmer and high if the right one is warmer.