Apple is trying to provide a method of securing device access that does not require an extra step for authentication.
The solution, the company suggests, would be to automatically use a sensor either hidden within the device or else repurposed from its usual role. Devices could recognize a fingerprint or finger vein pattern simply by waiting for the user to touch the display, which would hide the sensors on or behind the screen. A forward-facing camera could alternately look for retinal patterns or even recognize the facial features of owners when they're in the right position for use.
Notebooks could use the trackpad, palmrest and a webcam for a similar purpose. Apple goes so far as to suggest the possibility of recognizing the user's distinctive voice or even collecting DNA samples to recognize a user's genetic sequence. Biometrics could also be context-sensitive and detect the shape of a user's ear before allowing a call to go through, for example.