BOSTON — The Transportation Security Administration on Friday announced nine more U.S. airports that will receive body-scanning technology, as the U.S. heightens its effort to detect hidden explosives and contraband amid a threat highlighted by an attempted bombing on Christmas Day.

TSA security director Lee Kair said units will be fielded in the coming months at Fort Lauderdale, Fla.; San Jose, Calif.; Columbus, Ohio; San Diego; Charlotte, N.C.; Cincinnati; Los Angeles; Oakland, Calif.; and Kansas City.

They will join three machines going online Monday at Boston's Logan International Airport, and one being deployed next week at O'Hare International Airport in Chicago.

All are among 150 machines bought with money from the federal stimulus package signed by President Barack Obama last year. They join 40 machines already in use at 19 airports nationwide.

Both the new and existing machines will also now be in a primary position, meaning they will be the default screening equipment passengers face at a checkpoint. The existing machines have been in a secondary position, being used only when a passenger failed a metal screening or posed some other risk factor.

Passengers retain the right to opt out of a body scanning for a more intense but traditional screening. The Associated Press timed a body scanning at 25 seconds, and Kair said he did not expect them to take any longer than a passenger would have to otherwise wait for the X-ray of carry-on bags.