With the new sensors you don’t have to move your finger, just
press it against the reader. And like the sensor in the iPhone
5S, the sensors that will be in laptops and keyboards and other
phones can detect the ridge and valley pattern of your
fingerprint not from the layer of dead skin on the outside of
your finger (which a fake finger can easily replicate), but from
the living layer of skin under the surface of your finger, using
an RF signal. That only works on a live finger; not one that’s
been severed from your body.
This will protect you from thieves trying to chop off your finger
when they mug you for your phone (assuming they’re tech-literate
thieves, of course), as well as from people with fake fingers
using the fingerprint they lifted from your phone screen.
Good to know.