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so it wasn't that long ago that any mention of fingerprint scanning would
conjure up images of james bond breaking into a super villain's evil lair these
days it seems like everyone from secret agents to travel agents is carrying
around fingerprint scanners built into the smartphones that they're paying 30
bucks a month for but how exactly do they work and how they found their way
onto so many consumer devices well as it turns out typical fingerprint readers
use the same principle of capacitance as track pads and touch screens
so if you checked out our other episode on touch screens you'll know that they
typically function by detecting the difference in charge between the lower
layer of your skin which is conductive and the phone screen itself fingerprint
readers adapt this concept for personal identification by cramming loss of tiny
conductive plates into the space just below the scanner surface they're
narrower than the ridges that make up your fingerprints when you place your fingertip against the reader the sensors
can tell which portions of your finger their ridges are touching the sensor and
which are not because the small valleys are further away from the sensor which
decreases the capacitance the tiny plates will pick up the reader can use
these differences in capacitance to form a virtual image of the ridges of your
fingerprint now these scanners have actually been on phones since 2007 but
only really took off when apple released touch id with the iphone 5s in 2013.
however there are other types of fingerprint readers too optical scanners
use visible light to capture a more traditional image of your fingertips but
these are uncommon at least in portable devices due to their bulk and ultrasonic
fingerprint readers have the potential to be the next big thing these work
somewhat similarly to a bat's echo location the way they work out the
shapes of objects in the dark ultrasonic pulses emanate from the reader and hit
the ridges of your fingerprints then variations in the return signal are used
to construct a scan ultrasonic sensors not only have the advantage of a cool
marketing friendly name but they can also work through other materials
allowing them to be seamlessly embedded underneath the phone's surface for a
slicker look or to peer through the crud and moisture on your hands for better
reliability than their capacitive counterparts sounds great right but while many people
originally thought the fingerprint sensors as a highly secure technology
perhaps because of their association with spy films they certainly aren't
foolproof no matter exactly which variety you're using think of how the
scanner on your phone will work even though you don't place your finger on it
in exactly the same position every time this is because they only require a good
enough partial match to decide that it's your finger now this allows it to
recognize you from many different angles but it also means there's a small chance
of a false positive and even though master fingerprints are typically
secured in some way like how apple encrypts the touch id fingerprint and
stores it locally it's still possible to defeat fingerprint readers using
artificial molds that can be created if say some miscreant gets a hold of
fingerprints that you left on the wine glass so while the technology is super
convenient there are holes that have led most smartphone operating systems to
also require a password or pin which is especially important if you're
one of the few dozen or so people in the world that were born without fingerprints
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