I have a problem with noisy neighbours and want an app to measure and record the volume of their noise for possible legal action.

I prefer free-libre from F-Droid, but they don't have one.

Google Play has... hundreds of apps (one at US$100!). No idea which to choose, hopefully a free one without ads and data surveillance.

Web search results filled with sites I don't know/trust, and obvious SEO or AI slop.

So I'm asking folks here: anyone have any experience of a decibel meter app that's:

• preferably free-libre
• free-gratis (I might pay for a reasonably-priced pro version after I've tried out the free one)
• zero or tolerable ads
• zero or minial data surveillance

Thanks.