Which Sensors for detection of different things

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1

Trying to figure out the best sensors (preferably small as they are going into a compact structure) for sensing events. Heres the different events and what I have so far:

  1. Person Blowing across a surface: [Modern device Wind Sensor (pretty pricey would like something cheaper)…or will one of the barometers register a difference if someone blows on them?

  2. A lighter being lit: Using [this

  3. A few drops of water on a surface (cant figure this one out, looking to have a flat surface that a couple drops can be put on and detect), most are water level sensors and I just want to detect moisture on a surface

  4. An object placed on a surface, thinking of using a force-sensitive resistor

Any ideas, trying to keep total cost down](Amazon.com)](Wind Sensor Rev. C – Modern Device)

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Cost is obviously important to you: how much are you looking to spend (hint: that $17 is ridiculously cheap for a thermal anemometer)?

Size also apparently is: what’s the total volume you want to fit this stuff into?

If cost and size are really both that important, you’re probably going to have to design these at the component level. e.g., the anemometer raw sensor assembly can be built for about $1.00 in parts and occupy the volume of about a penny.