(FORTUNE Magazine) – Biometric devices, designed to keep your PC and its sensitive data secure from prying eyes, are popping up on more and more desktops. These systems--once the stuff of science-fiction movies--replace typed passwords with software and hardware that identify us by our fingerprints, voiceprints, face prints, or retinal patterns.

U.are.U, one of the slickest biometric devices I've seen, is manufactured by Digital Persona Inc. of Redwood City, Calif. It's a small, crescent-shaped fingerprint scanner that attaches to the universal serial bus port of computers running Windows 95 or 98. Although I was skeptical about the claims it made, U.are.U turned out to be one of those rare products--a gadget that installed easily and worked exactly the way it should.

After I loaded the software from a CD-ROM, I plugged the scanner into my computer's USB port and "enrolled" myself, which meant placing one of my fingers on the scanner's clear-plastic pad four times. U.are.U analyzes your fingerprint and stores it as a 300-byte mathematical formula on your hard disk. You can enroll one fingerprint or all ten, but the manual recommends that you register at least one finger on each hand, just in case you lose the use of one of your digits. (A gruesome thought, no?) That done, a U.are.U prompt appears when you turn on your computer asking you to put your finger on the scanner. If it doesn't recognize your print, it won't boot up. By default, U.are.U also installs a screensaver that starts up when you haven't touched the PC for a set period of time. Instead of using a password to restore the screen, you touch your finger to the scanner.

As the first user on a U.are.U system, you also become the fingerprint "administrator," which is a bit like being the sergeant in Central Booking. You can enroll your family or co-workers by setting up accounts and having them record their fingerprints, just as if you were setting up regular user profiles under Windows.

While U.are.U had no problem enrolling my fingerprints, my wife had to record her prints twice before the program was satisfied that it had a recognizable profile. The staff at Digital Persona said this isn't unusual. Because women have smaller fingers, the ridges of their prints are closer together and harder to sample. Likewise, children are more difficult to analyze than adults. But once we were all enrolled, U.are.U recognized each of us instantaneously without a mistake. My wife was worried that using hand cream would gum up the works, but according to the company, the opposite is true--the oilier the fingerprint, the better.

The $199 U.are.U Deluxe package includes a second CD with a program called Private Space that allows you (and other users that you authorize) to set up encrypted disk partitions that show up as new disk drives in Windows Explorer. Your fingerprint unlocks the encrypted files--otherwise they're hidden from everyone else. This is great for shared computers. You and your co-workers can all use a PC with the expectation of privacy, or you can give your kids carte blanche to use the family computer at home without worrying that they'll trash your income-tax or investment records.

After using U.are.U for several days, I was really pleased. Unlike some fingerprint scanners, U.are.U doesn't care how you line up your finger over the scanner's window--it can read a print right-side up, upside down, or sideways. The only downside, which is true of U.are.U and its competitors, is that fingerprint reading requires a fairly expensive gadget that's a pain to carry when you're on the road.

If you're interested in cheaper, more portable security, try a voice-recognition program such as Saflink's SaftyLatch (see "Keep Your Secrets Safe with Voice-Activated Software" in the fortune.com archive for March 1). Voiceprints aren't as secure as fingerprints, and those machines are finicky about background noise and microphone placement--but they're easy to set up and take with you. For more information on U.are.U, contact Digital Persona at 877-378-2738 or surf to www.digitalpersona.com.

--Michael J. Himowitz