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Yeah I want that for detecting when my furnace cycles. One mic could probably cover everything in the utility room.

With multiple outdoor microphones I'd love to build a ShotSpotter, but I'm not good enough at audio to know how practical that is.

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For a forced-air furnace, I put a hinged piece of cardboard over a room vent with a paperclip switch. When the furnace blew, the cardboard would rise and the switch would open. Simple and effective. It doesn't measure the burn cycle of the furnace exactly, but it was close enough for me.

Sounds like a story I've heard about a conveyer belt and a large fan.

I like simple solutions to simple problems

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