And within the past few weeks, liquids including hair gel, deodorant, and mouthwash were barred from carry-on luggage after British authorities foiled a plot to blow up 10 U.S.-bound planes. Only such critical items as insulin and baby formula are allowed.
Critics contend that all of these new security measures are largely a waste of time and effort.
"This is a game we certainly cannot win," said Bruce Schneider, a security technologist and author based in California. "That's because it's not a fair game. The terrorists get to see what we do, then react."
Schneider said the best defense against terrorist attacks, either on airlines or in any setting, is intelligence, which was the most important factor in disrupting the plot in Britain.
Before the 2001 terrorist attacks, the airlines were responsible for baggage screening and hired their own private contractors to do the work. But those have been replaced by federal Transportation Security Administration personnel, who randomly pull passengers aside to search their carry-on luggage for suspicious objects.
Logan International Airport is now armed with a $146 million baggage-screening system, one of the most sophisticated of any of the nation's airports. The Massachusetts Port Authority operates Logan, along with the Tobin Bridge, and the Port of Boston.
Massport has been criticized for being a haven for patronage jobs. Some say the authority was transformed when Craig Coy, a former Coast Guard officer and helicopter pilot, was appointed its chief executive in 2002.
"That appointment immediately changed the culture at the top of the organization," said Christopher Anderson, president of the Massachusetts High Technology Council, who also serves on the Massport Security Advisory Council. "The executive leadership has a different culture and level of professionalism."
Under Coy's direction, Massport now has full security "from the time you park to the time you board the plane," added Anderson, a Westford resident.
Coy served until July 1, when Logan Airport Director Thomas Kinton Jr. took over as CEO.
Anderson said Massport demonstrated its strengths Aug. 16, when a jet was forced to land at Logan because of an unruly passenger. Massport officials worked with the federal agents to isolate the passenger and her baggage.
"The question is, 'How do you marry these new security technologies with passenger interruption?' That will be a continual process," Anderson said.
Security has been increased in other modes of travel:
On the seas. Tankers carry up to 6 million gallons of liquefied natural gas through Boston Harbor, close to residential areas, into a terminal in Everett. Boston Mayor Thomas Menino has long complained that the city's fire department doesn't have the resources to respond should an explosion happen on one of the tankers. The Coast Guard now requires that the LNG tankers have a one-mile buffer front and back.
In 2002, the state Legislature approved legislation creating a 500-foot buffer zone around Logan, and also requiring any clammers working on the shoreline near Logan to submit to a criminal background check.
Rail and bus. The July 2005 bombings in the London Subway brought about sweeping changes to the security at the Massachusetts Bay Transportation Authority. All MBTA employees are given routine terror-awareness training, including how to respond to passengers being taken hostage and explosive devices.