I have a rotation of instrumental ambient playlists like Medieval Ambient and Dungeon Ambient. We're so used to them, it's strange not to have them when we're on vacation.
I did this several years ago. It worked well for a few months, and then burnt out the phones. They're not meant to run 24/7 and on a charger the whole time.
People like to feel that there is justice and that bad guys get caught. Serial killers and the source of info (mostly police departments) makes for low hanging fruit. To get less biased info would take more work. It is possibly different outside the US.
The Tile app (you can use without buying anything) can turn on the ringer and set full volume. My partner and I use it to find each other's phones. There are probably other apps that do that, too.
I tried it, and it worked well for several months, and then the phone died. They're not made to run and be on for that amount of time.