RICHMOND, Calif.—California officials are outfitting preschoolers in Contra Costa County with tracking devices they say will save staff time and money.

The system was introduced Tuesday. When at the school, students will wear a jersey that has a small radio frequency tag. The tag will send signals to sensors that help track children's whereabouts, attendance and even whether they've eaten or not.

School officials say it will free up teachers and administrators who previously had to note on paper files when a child was absent or had eaten.

Sung Kim of the county's employment and human services department said the system could save thousands of hours of staff time and pay for itself within a year.

It cost $50,000 and was paid by a federal grant.