So do a rising number of jobs. Ingersoll Rand Recognition Systems of Campbell, Calif., a major manufacturer of hand readers, says more than 100,000 of its devices are used at workplaces ranging from an Ohio ice-cream plant to a Florida golf club to a resort-construction site on the Macau peninsula of China.

To use the scanners, an employee enters an ID code or swipes a card and then places his or her hand on a sensor. The machine gauges the hand's size and shape and determines whether it matches what's on file for that code or card. The "hand geometry" images aren't comparable to the detailed fingerprints used in law enforcement, says Tom Brigham, an Ingersoll Rand spokesman.

Some employers - such as airports, shipping ports, research facilities and nuclear plants - tend to use the scanners primarily for security. But others see them more as tools to make payroll easier, more accurate and harder to fudge.

For public schools in Birmingham, Ala., hand scanners were the answer to a judge's call for a better time-keeping system, says schools spokeswoman Regina Waller. The school system installed the devices after paying $4 million to settle an overtime-related lawsuit, in part because some paper time sheets were lost or otherwise unverifiable, she said.

People First Inc., a Florida-based payroll-processing firm, finds that hand-scanner systems can cut clients' expenses by about 10 percent, says president Barbara Flynn. The scanner systems stop colleagues from clocking each other in, save supervisors hours of work checking time cards and guarantee workers that their true hours are being logged, she said.

"It protects the company from liability ... and it protects the employee from being taken advantage of," she says.

But privacy advocates find such systems troubling. The more personal information gets collected, the more is at risk if the data is hacked into or otherwise exposed, says Lillie Coney, associate director of the Washington-based Electronic Privacy Information Center.