Sound Level Warning Device: Suggested shopping list

You said you want it to be accurate. How are you going to calibrate it?

To be more specific, I want it to be fairly accurate. Not laboratory-level by any means. I read a post where the person used a dB meter app on their phone to get a baseline and adjusted it from there. Hopefully that will work for me.

Googling “diy sound level meter” produces 13,500,000 results.

Just pay little attention to the instructables articles. They can often be of little value - untested crap.

As for your shopping list, add this:

Thank you for the advice! Is that in addition to, or replacing the MEMS microphone breakout? If it helps, it will be almost completely enclosed in a plastic casing, I picked the MEMS microphone because (unless I’m mistaken) it said it would not require much of a hole for sound to get through, that it could be pressed right up against the enclosure and still get good sensitivity.

The enclosure is a 6"x6" “rounded pyramid” form. Similar to the following picture, but made of plastic.