The Galaxy S5 is one of the few smartphones that offers a fingerprint scanner as a means for authentication. Incorporated into the Home button, Samsung reduces cost and size by using a swipe-style sensor. Since the sensor is too small to scan your entire fingerprint at once, you must slide your finger over the sensor, which takes a series of measurements and then stitches them together via software. The drawback to this approach is reduced accuracy, as the process can be sensitive to the speed and angle with which you slide your finger over the sensor and algorithmic artifacts created while stitching the individual images together. The passive capacitive sensor in the S5 is also less accurate than the active capacitive sensor technology Apple acquired from AuthenTec in 2012. It will be interesting to see how well the S5’s sensor works compared to Touch ID.
Registering a fingerprint is a simple affair: just swipe your finger across the sensor eight times. Unlike Apple's Touch ID setup process that requires you to vary how the finger is placed on the sensor, the S5 doesn't ask for any variation in how you swipe during its setup procedure. Up to three fingerprints can be stored, versus five for Touch ID.
When the S5 first launched, the fingerprint scanner was ridiculed for its poor accuracy. In our initial tests, we saw our success rate hover around 50%. However, subsequent software updates have improved accuracy substantially. I'm actually quite surprised at how well it works now, with accuracy nearly identical to Touch ID. I say nearly because the S5's swipe sensor is still less forgiving than Touch ID when it comes to finger orientation. Still, I found that I could vary the angle of my finger by up to about 30º before the scan would fail and even varying the swipe speed didn't affect accuracy.
With performance nearly equal, the distinguishing factor between Apple's Touch ID and Samsung's implementation is ease of use. Only requiring a finger to touch the sensor, in any orientation, makes Touch ID more pleasant in practice. The S5's sensor is bit awkward to use because your finger needs to be swiped over the sensor, which is located close to the bottom edge of the phone. Swiping a finger lengthwise either requires the use of two hands or setting the phone on a flat surface. The scanner can actually be used while holding the phone normally with one hand by swiping your thumb diagonally. This method is much more convenient and natural, although accuracy decreases slightly.
By default, the fingerprint scanner can only be used to unlock the phone or access Samsung services. However, with the right apps installed, it can also be used for authenticating PayPal transactions and other FIDO Ready online services, adding to its usefulness.
Similar to Apple's Touch ID, the S5's fingerprint scanner didn't work exceptionally well when it first shipped. But with some additional fine tuning in software, both biometric solutions have matured into useful authentication features.