I seem to recall reading somewhere that 'everything' is a thermometer, on the basis that many things behave differently at different temperatures. You can also

I seem to recall reading somewhere that 'everything' is a thermometer, on the basis that many things behave differently at different temperatures. You can also use an LED as a light sensor. and I also came across a YT vid of a console that used a piezo electric speaker for motion sensing. I wonder if you could use a track pad to pick up sound.