There are many different identification technologies available, many of which have been in widespread commercial use for years.

There has developed considerable interest in biometric identification systems, which use pattern recognition techniques to identify people using their physiological characteristics. Fingerprints are a classic example of a biometric system; newer technologies include retina and iris recognition. While appropriate for bank transactions and entry into secure areas, such technologies have the disadvantage that they are intrusive both physically and socially.

Though these are useful in high-security applications (they make the systems look more accurate), they are exactly the opposite of what is required when building a store that recognizes its best customers, or an information kiosk that remembers you, or a house that knows the people who live there. Face recognition from video and voice recognition have a natural place in these next-generation smart environments -- they are unobtrusive (able to recognize at a distance without requiring a 'pause and present' interaction), are usually passive (do not require generating special electro-magnetic illumination), do not restrict user movement, and are now both low-power and inexpensive. Perhaps most important, however, is that humans identify other people by their face, therefore are likely to be comfortable with systems that use face recognition.