How are iPhones still findable even when turned off

XDA

By Mahmoud Itani

Published Oct 6, 2021

iOS 15 brought a handy feature to some supported iPhone models. It allows users to find their iPhones even when they're turned off.

Apple revealed iOS 15 back in June, during its opening WWDC21 keynote. While the update wasn't as packed as we had hoped it would be, it still brought some significant improvements to the table. One of these additions is Find My support, even when iPhone is turned off. However, it is only available on select models. So why isn't this feature supported on all iPhones running iOS 15, and how does it exactly work?

According to a post by Naehrdine:

All the iPhone needs to have Find My enabled while it is "off" is some basic power control as well as a Bluetooth chip that can send Bluetooth LE advertisements. Moreover, these advertisements require secret key material bound to the Apple ID on the iPhone.

So when a supported iPhone is powered off, Find My runs in the Bluetooth chipset via a custom applet. The rest of the device is completely off, so only this chip is awake and running on low power to transmit BTLE beacons. While the article mentions AOP (always-on processor), Hector Martin says in a Twitter thread that the Find My service, while powered off, has nothing to do with it.

If you're wondering why all iPhones running iOS 15 aren't supported, it seems that the feature requires iPhones to write a series of pre-computed cryptographic beacons to the UWB chipset. So older iPhones with no U1 chip can't support the feature. This mechanism is similar to that of the AirTag, and Naehrdine states:

On the AirTag, this key material is stored via the U1 chip. Apple calls the nRF on the AirTag "Durian" for a reason. They don't like it, they don't trust it, but it's cheap and low-power. Most time, U1 is on sleep, and from time to time they wake it up.

As a result, powered off iPhones can still be found when approached by another internet-connected, Find My-enabled device. The dead iPhone securely transmits the required identification information to the connected device via Bluetooth. The latter then sends the data to Apple servers. The owner of the dead iPhone can then see the reported location on the map, where another connected device had passed.

XDA Basics: How to use Find My on Mac to Find your Lost Apple Device

Find My while powered off is a significant upgrade to the existing feature. Not only does it help you locate your iPhone after it shuts down, but it also allows you to track thieves even if they power off the device.

What do you think of this new feature? Have you ever depended on Find My to locate a lost or stolen device? Let us know in the comments section below.