The lock-and-key system dates back to about 2000 B.C. Nowadays, though, there are a variety of electronic access systems that are far more foolproof -- and, starting at around $2,000, they're not that much more expensive.

Beyond merely granting passage, in conjunction with a computer many of the systems listed below log who enters a designated area and when. They also can allow or disallow employees as they're hired and fired, and can restrict passage to certain times, areas, or individuals.

The most secure are the biometric systems, whose sensors depend on an individual's unique physical attributes -- the retina of an eye or the timbre of a voice. Other modes have their own attractions. A magnetic card, for example, won't bar a person with laryngitis.

Here are some systems selected as examples by Inc.:

* * *

Hand Geometry

Recognition Systems, San Jose, Calif.; 408-257-2477

Scanner analyzes 3-D image of hand pattern. User enters personal ID number (PIN).

Benefits: Can't be stolen. Authorization criteria allow for Band-Aids or jewelry. Users report it's the most friendly, easy-to-use biometric mode.

Drawbacks: User needs to memorize PIN.

Basic installation cost: $3,500 to $5,000

Handwriting

Digital Signatures, Columbia, Md.; 301-730-8250

Analyzes characteristics of signature via pen-and-tablet interface with dedicated computer.

Benefits: Can capture and print out signature for other verification applications. Most often used to allow or deny access to proprietary data and to authenticate electronic mail.

Drawbacks: Process is much slower than others. Users may be concerned about invasion of privacy. Forgery possible.

Basic installation cost: $1,200 to $2,000

Magnetic Card

Northern Computers, Milwaukee; 800-323-4576

Magnetically encoded card passes through slot of reader.

Benefits: Does not require dedicated computer. Can be incorporated into photo-ID badge for added security. Reader unit can be coded to exclude any outstanding card.

Drawbacks: Card can be used without authorization, unless PIN also required. Card can be copied. Can be balky in cold climate. Magnetic strip can rub off over time.

Basic installation cost: $2,000 to $3,000

Wire-Embedded Card or Key

Sensor Engineering, Hamden, Conn.; 203-777-7444

Card or key with identifying code is passed through or inserted into reader.

Benefits: Cannot be copied. Not affected by cold. Code can't rub off. Provides enhanced security, because encoding is done by manufacturer rather than in field.

Drawbacks: Can be used without authorization. (Like others, it can be used with a PIN.)

Basic installation cost: $2,000 to $3,000

Touch-Free Transmitter

Radionics, Salinas, Calif.; 408-757-8877

Proximity of electromagnetic waves detected by sensitive receiver.

Benefits: Allows hands-free operation. Vandal-resistant because there's no outside reader. Operates through glass or wall. Can't be duplicated. Can be incorporated into ID.

Drawbacks: Anyone can use it, unless PIN required (which would negate the hands-free feature). Transmitting unit larger than a key but not larger than a magnetic card.

Basic installation cost: $4,500

Voice Recognition

International Electronics, Canton, Mass.; 617-821-5566

Matches spoken password with stored vocal pattern.

Benefits: Recording or impersonation have never fooled computer in tests. Relatively inexpensive for a biometric system.

Drawbacks: User needs to memorize and enter PIN. Some users report feeling uncomfortable talking to a wall.

Basic installation cost: $2,000 to $3,000

Retinal Scanner

EyeDentify, Beaverton, Ore.; 503-645-6666

Infrared beam analyzes blood-vessel pattern of retina and matches it with stored record.

Benefits: Can search entire database for match. Can't be fooled: even identical twins have unique retinas. Hands-free operation (without PIN).

Drawbacks: Glasses must be removed. Has been perceived by some users as unsanitary, and suspected as covert test for drug use.

Basic installation cost: $6,500 to $8,500

-- Researched by Chris Caggiano