Touch ID is a fingerprint recognition feature that was designed and firstly released by Apple Inc. and used mainly in Apple’s mobile devices like iPad and iPhone. And now more and more smartphone manufacturers start to make Android handsets with Touch ID. As one of fingerprint recognition technique, how Touch ID works?
Touch ID is built into the home button, which is built of laser-cut sapphire crystal, which does not scratch (scratching would prevent Touch ID from working). It features a stainless steel detection ring to detect the user's finger without pressing it. There is no longer a drawing of an app icon in the home button, nor is it concave.
The sensor uses capacitive touch to detect the user's fingerprint. The sensor has a thickness of 170 µm, with 500 pixels per inch resolution. The user's finger can be oriented in any direction and it will still be read. Apple says it can read sub-epidermal skin layers, and it will be easy to set up and will improve with every use. (From Wiki)