Fingerprints remain constant throughout life. Good fingerprint scanners have been installed in PDAs like the iPaq Pocket PC; so scanner technology is also easy. Might not work in industrial applications since it requires clean hands.
Fingerprint identification involves comparing the pattern of ridges and furrows on the fingertips, as well as the minutiae points (ridge characteristics that occur when a ridge splits into two, or ends) of a specimen print with a database of prints on file.