San Diego, California - For the first time, the identities of foreigners leaving the United States through a land border are being checked with high-tech biometric equipment capable of reading faces and irises.

U.S. Customs and Border Protection has started screening pedestrians crossing into Mexico at Otay Mesa in a field test aimed a determining how the readers works in a land setting. The new procedures are part of a move by the U.S. Department of Homeland Security aimed at gaining greater information about who leaves the United States.

The test, which is scheduled to conclude on April 29, is part of an effort that uses biometrics to crack down on identity theft as well as to keep track foreigners who remain in the United States with expired visas. For the next few weeks, all pedestrians leaving San Diego through Otay Mesa will be subject to screening, but only foreigners will have their identities documented through iris and facial recognition technology. The testing is taking place Monday-Friday, from 7 am to 10 pm.

Biometrics measure a person's unique physical characteristics, through methods that include the reading of fingerprints, irises and facial structure. CBP has been verifying travelers' identities through fingerprints since 2004.

The new southbound inspections at Otay Mesa began earlier this month, and represent the second phase of a test that was launched in December. The first phase has involved using readers to capture biometric information of non-U.S. citizens entering the United States on foot through the Otay Mesa Port of Entry, creating a database for the test.

According to CBP, 9,000 pedestrians a day cross into the United States through the Otay Mesa Port of Entry, while about 6,000 leave the country. "The majority of the technology is meant to be minimally intrusive on the traveler," said Charmaine Rodriguez, assistant port director at Otay Mesa. The test data is being kept in a local database and not being shared with other law enforcement agencies, she said.