[bnc319]

I'm guessing this works exactly the same way as Apple's "Findable After Power Off" feature [1]. If the phone "dies" the battery still has some reserve to display the "charging needed" screen when the power button is pushed, along with sending location. Additionally, it can use the Find My network [2] where other devices that are powered on can relay the proximity device's location using their own location.

1. https://www.theverge.com/22697218/iphone-apple-ios-15-find-m... 2. https://developer.apple.com/find-my/