With Windows Hello, your Lumia 950 or 950 XL can unlock your phone using iris recognition.
Set up a sign-in PIN. On Start, swipe over to the All apps list, and then select Settings > Accounts > Sign-in options > Add.
Under Require sign-in, choose how often your phone requires sign-in.
Set up Windows Hello. Select Set up, and then follow the instructions. If you wear glasses, remove them during the first setup. After that, select Improve recognition, put your glasses back on and follow the instructions again.
To unlock your phone, press the power button. Hold the phone up in front of your face (just like during the setup), and wait for your phone to recognize you. If that doesn't work, swipe up on the lock screen and enter your sign-in PIN.