While the cautionary measure will begin in California, the Daily News of Los Angeles said Sunday, the "new generation" monitors will soon be installed at ports across the nation and along the border.

Officials from the U.S. Domestic Nuclear Detection Office said the monitors ultimately will scan nearly all cargo entering the United States.

"We have made tremendous improvements in looking for these types of materials," detection office official Vayl Oxford said.

"I think that security at our borders is increasing every day and the likelihood of someone bringing in threatening materials is diminishing on a daily basis."

Yet some have criticized the move, alleging the devices will be no better than monitors currently being used. The Daily News said those critics have called for more stringent measures to ensure border security.