When playing with piezoelectric buzzers as potential microphones for my #Feedbass! project, I noticed they are very sensitive to temperature fluctuations. Like, it would detect me waving a hand nearby.

At some point, I soldered a pair of LEDs to a buzzer, just to see how hard do I have to push it to make them light up. And checked the temperature sensitivity as well, and I was shocked! Heating or cooling the buzzer quickly enough makes an LED glow!

I totally wouldn't have been surprised by a little bit of pyroelectricity from essentially anything. But being strong enough to light up a LED is totally nuts! 

I'm not sure if it is pure pyroelectricity. Almost certainly, piezoelectricity can be involved. Because ceramic and metal plate have different coefficients of expansion, hence heating the buzzer will cause it to behave like a bimetallic plate, and thus create mechanical stress and cause some piezoelectric voltage to appear.

Now I am wondering, what cool project can be done based on this effect. A thermal imager, maybe?

https://en.wikipedia.org/wiki/Lead_zirconate_titanate

which is indeed used in thermal cameras. Cool!