Bomb experts say that security checks are probably more likely to find the device that detonates a liquid bomb than the liquid explosive itself.

NPR: It's Hard to Spot a Liquid Threat to Airline Safety

On occasion, such as a liquid bomb scare in August 2006, the TSA has expanded the list, banning large containers of liquids and gels.

CNN: TSA to allow pocketknives, some sports equipment

On occasion the TSA has expanded the list, as it did after a liquid bomb scare in August 2006 when it prohibited bringing large containers of liquids and gels on board aircraft.

CNN: March 7, 2013 -- Updated 0312 GMT (1112 HKT)

During his term, the agency loosened restrictions on some items -- such as cigarette lighters, matches and small scissors -- while imposing limits on liquids and gels because of the August 2006 liquid bomb scare.

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The following year, in 2006, U.K. authorities interrupted a plot to bomb trans-Atlantic airliners using liquid explosives carried in bottles.

WSJ: A Killing Puts U.K. on Guard for Terror

Until recently the only equipment for spotting a suitcase bomb was an unwieldy machine the size of a refrigerator, using liquid nitrogen to cool crystal detectors down to 300 degrees below zero and taking hours to produce a reading.

FORBES: Stopping Porta-Nukes

Until recently the only equipment for spotting a suitcase bomb was an unwieldy machine the size of a refrigerator that used liquid nitrogen to cool crystal detectors down to 184 degrees Celsius below zero and took hours to produce a reading.

FORBES: Stopping porta-nukes