Learned a lot from this piece.

Capacitance readers are more complex, instead creating an image of your fingerprint by measuring the differences in capacitance between the ridges and valleys of your fingerprint. They leverage the electrical conductivity of your sub-dermal skin layer, and the electrical insulation of your dermal layer (the one where your fingerprint is). Your fingerprint is effectively a non-conductive layer between two conductive plates, which is the very definition of a capacitor. The fingerprint reader senses the electrical differences caused by the varied thickness of your dermis, and can reconstruct your fingerprint.

The Touch ID sensor in the iPhone 5s is a capacitive reader, embedded in the home button. That was a good choice on Apple’s part, since capacitive scanners are more accurate and less prone to smudgy fingers, and can’t be faked out with a photocopy of a fingerprint.

The question I have is, are capacitance readers susceptible to Play-doh copies of your fingerprints. This is a technique used to defeat some fingerprint technologies.

UPDATE: And the answer is, a resounding no. Need a live finger for capacitance to work.