With iOS 15, your iPhone is still traceable through the Find My network even when the device is powered off. It seems that with iOS 15, the phone is not really fully ‘powered off’, it stays in a low-power state and acts like an AirTag, allowing any nearby iOS device to pick up the Bluetooth signal and send back its location.
In fact, Apple says the location tracking will even keep working whilst the phone is reset to factory settings with Activation Lock enabled.
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