Biometric security -- which employs systems that read people's fingerprints or compare their voiceprint or retina scans to information in data banks in order to authenticate them -- is being heavily used in some of the United States' most critical installations.

For example, the United States Department of Defense is focusing strongly on biometric security. The U.S. Army Biometrics Task Force has selected Raytheon to provide biometric-related services and support.

How reliable are biometric systems, anyhow? What happens if you have a cold or haven't had enough sleep and your voice is hoarse, your nose is running, and your pupils are contracted or dilated? Can security systems mistakenly identify you as a terrorist or a person of interest in an ongoing police investigation?

That's where biometric systems run into trouble...