Biometric devices are security measures that use an element of a person's unique biological properties to identify him, rather than a more easily copied identifier such as a password. Biometric devices typically use a component of biology that is difficult to use fraudulently, such as fingerprints, handprints, a voice pattern or the retina of the eye. It is fairly safe to assume that if a person has the correct biometrics, he is using the correct identity.
Biometric devices are typically used to protect computer devices and locations from unauthorized access. The user is required to produce the requested biometric data, either by holding the appropriate body part to a scanner or by producing a voice sample. An authorizer can require users to pass multiple biometric tests.
The downside of biometrics is that an authorizer cannot remotely allow access to the device or location for another person. The authorizer must appear in person to gain access.
There are ways to bypass biometric systems. People can copy fingerprints, and they can record voices. A retina scanner is considered one of the most secure biometric devices because there is no known way to alter the pattern of a human retina, as of 2015.