For security reasons, when you make certain requests of Siri — such as checking your email or unlocking a HomeKit door lock — she’ll respond that you need to unlock your iPhone first, usually presenting you with the keypad, so you can either punch in your passcode or use Touch ID to authenticate. However, if you often find yourself making these requests, you’ll be happy to know that there’s a way to do it a bit quicker, as long as you’re using a Touch ID-equipped iPhone.
If you activate Siri by holding down the Home button with the same finger you use for Touch ID, and make your request while holding the button, Siri will recognize your fingerprint as you make the request, performing the action without asking you to unlock your iPhone. Afterward, your iPhone will still remain locked unless you tap on the Siri results to open something like an email message or a web link. In fact, as long as your finger is resting on the Touch ID sensor when you make the request, Siri will accept that as valid authentication and not prompt you to unlock, so this technique can even be used when making requests with “Hey Siri” on newer iPhone models as well.