The local office of the U.S. Customs and Border Protection office has a new weapon in its arsenal of devices designed to thwart attempts by would-be terrorists — or anyone else — to smuggle radiological material into the country.

The $2 million drive-through Radiation Portal Monitor has been in operation for the past week or so at Fort Armstrong, across from Restaurant Row, and has been used to screen 300 to 500 vehicles a day at Pier 1, where most freight from foreign countries arrives in Hawai'i, said Customs spokesman Jim Kosciuk.

"The best way to prevent a terrorist attack is by preventing terrorists or terrorist weapons from entering the U.S.," said Hilda Montoya, acting director of the Port of Honolulu.

The device was designed to detect materials that could be used to build full-on nuclear bombs as well as "dirty bombs," but is so sensitive it can detect minute amounts of radiation such as that found in earthenware, smoke detectors and agricultural products.

"It will also provide a 'hit' on people who have undergone nuclear medicine treatments," Kosciuk said.

Two exit lanes at the harbor lead through the machine, and if it sounds an alert, a red light will remain on and Customs and Border Protection officers will "begin a dialogue" with the driver of the vehicle that has been flagged, Kosciuk said.

Other gadgets the CPB officers have at their disposal can quickly identify the the various radioactive isotopes that have triggered an alarm and, if need be, information can be transmitted electronically to agency scientists on the Mainland to determine exactly what has caused the alarm to sound.

Response to a positive hit can range from a conversation with the person driving the car or truck, to checking manifests against the actual cargo in a shipping container and ultimately off-loading all of the cargo and going through it piece by piece, Kosciuk said.

Montoya said the new radiation detector is a "passive device," meaning it does not emit radiation. She said her agency worked closely with the state health and transportation departments in having the device installed.

Customs and Border Protection began using the monitors elsewhere in 2003, Kosciuk said.

Reach David Waite at dwaite@honoluluadvertiser.com.