Biometric Devices

Biometric devices are used to control entry based on the measurement of one or more of an individual’s physical or personal characteristics. Because most entry-control devices using this technique rely on measurements of biological characteristics, they have become known as biometric devices. Characteristics such as fingerprints, hand geometry, voiceprints, handwriting, and the patterns of blood vessels on the retina have been used for controlling entry.

Typically, when individuals are enrolled in such a system, several reference measurements are made of the selected characteristic. These measurements are stored in the device's memory or on a card. Whenever that individual attempts to enter, a scan of the characteristic is compared with the reference data template. If the two match, entry is granted. Rather then verifying an artifact, such as a code or a credential, biometric devices verify a person's physical characteristic, providing a form of identity verification. Biometric devices are sometimes referred to as personal identity-verification devices.

Fingerprint-verification devices use one of two approaches. One is recognition of the pattern of whorls, loops, and tilts of the referenced fingerprint, which is stored in a digitized representation and compared with the fingerprint of the prospective entrant. The second approach compares the endings and branching points of ridges and valleys of the referenced fingerprint with the fingerprint of the prospective entrant.

Several devices use hand geometry for personnel verification. These devices use a variety of physical measurements of the hand, such as finger length, finger curvature, hand width, webbing between fingers, and light transmission through the skin to verify an individual’s identity. Two- and three-dimensional units are available.

Retinal scanning is based on the premise that the pattern of blood vessels on the retina of the human eye is unique to an individual. While the eye is focused on a visual target, a low-intensity infrared light beam scans a circular area of the retina. The amount of light reflected from the eye is recorded as the beam progresses around the circular path. Reflected light is modulated by the difference in reflectivity between blood-vessel pattern and adjacent tissue. This information is processed and converted to a digital template that is stored as the eye's signature. Users can wear contact lenses when their eyes are scanned. Persons with eyeglasses should remove their glasses before their retina is scanned.

Frequently, an automated entry-control system uses combinations of the three types of entry-control devices (electronically coded, credential, and biometric). Combining two different devices can significantly enhance the system's security level. In some cases, combining devices can reduce verification times.