Apple is further tightening the integration between iPhone and Apple Watch in iOS 15. If you have an Apple Watch paired with your iPhone, you will be able to use Siri to trigger tasks even if your iPhone is locked.
This new feature in iOS 15 further builds on the “Unlock with Apple Watch” feature that Apple debuted in iOS 14.5. Currently, if your iPhone is locked and you ask Siri to change any system settings or read a message, it will first prompt you to unlock your iPhone using Face ID or Touch ID. This beats the point of asking Siri to change any system setting or reading a notification as you would still be forced to use your phone.
You will have to ensure that your Apple Watch is passcode protected and unlocked for Siri to work on your iPhone without having to unlock it first. This is a small change from Apple, but one that will make Siri that much more useful, especially since the voice assistant can now process many tasks on-device without an active internet connection. This means Siri will be much faster at doing certain tasks in iOS 15.
There are plenty of other new features in iOS 15. The public release of the OS is scheduled for September. If you cannot wait until then, you can install the iOS 15 beta on your iPhone to take try out all the new features today itself.