Turns out it wasn't useful because someone else had taken it to lost and found within a few minutes of me losing it, before I knew I'd lost it. But it was a good idea.
Maybe I'm misremembering, but for example my esphome proxies in HA will show nothing for ages at night while my phone isn't being interacted with.
If the phone is lost, it's probably not super awake lol
That's an entirely different technology, and if you look at it from an RF lens, a highly impressive one.
Make your phone alert when one walks into a room within several meters