Airport screeners are using new technology to find explosives instead of hunting for tweezers, Department of Homeland Security Secretary Michael Chertoff said Friday. Locked and armored cockpit doors and air marshals on planes are part of a switch in main security concern from hijackers to people who might want to blow up airplanes, Chertoff said in a speech at an event here hosted by the Commonwealth Club. "The things we're really worried about are explosives," Chertoff said. Airport screeners are being retrained "to move them away from looking for things like nail clippers to more sophisticated chemicals and detonating devices," he said. "We have now set an aggressive timetable to complete deployment of the TWIC card," Chertoff said. "Our goal is to have these cards in the hands of port workers this year with those workers undergoing background checks. "The card will be for hundreds of thousands of people who need to access ports on a regular basis. "It will include biometric technology so we can make sure that the cardholder is really who he or she says that he or she is, and will give us the confidence about who is entering our ports," Chertoff said.