Device that support Find My iPhone when it's turn off

 iOS 15: Here are the devices that support Find My when turned off

It uses Bluetooth technology to send the location of a lost device to other Apple devices nearby. This way, users can see the location of an iPhone, iPad, Mac, or Apple Watch even when it’s not connected to the internet.

Find my iPhone ios 15

iPhones with U1 

iPhone 11

iPhone 12

iPhone 13 

iPhone without U1 

All older devices  

If you have an older iPhone or even any iPad model, you will still be able to use Find My when your device is offline but not if it’s turned off. 

It’s almost as if this feature turns your iPhone into an AirTag.