Access control is the ability to allow or deny the use of a certain object by a certain person or entity. Access control machine can be used in managing physical objects (such as a movie theater, to which only people with tickets are allowed in) or digital objects (for example, a private text document on a computer, which only certain users should be able to read).
Because every person’s fingerprint, iris, voice, retina, face, hand, vein and signature are unique, a biometric time clock provides a quick, accurate, and reliable way to record who is accessing an object or place. That is why many companies now employ biometrics (systems that identify people based on a body part).
In recent times, there are large number of biometric systems that are commercially available. Such biometric systems are based on unique characteristics of human being. The most common, reliable and successful system is the one based on fingerprints. Users are supposed to put their thumb/index finger (or any specified finger) in the finger reader. The system then compares the fingerprint that is read with the one in the central database for authentication.
Most biometric systems do not keep an image of the fingerprint but a template. A template is basically a number that is calculated based on various characteristics of the fingerprint. This is done so that persons may not sneak unauthorised images of fingerprints into the database. When a fingerprint is to be matched, its "template number" is computed and compared with that stored in the database. Most systems allow for dry, greasy, chaffed and minor cuts on the fingers. The other biometric systems are based on retina of the eye, palm, photograph or voice pattern recognition. The palm-based systems take the image of the palm from various angles and compare them.