Because of a failed terrorist attack involving the use of liquids in 2006, the TSA has instituted a regulation restricting liquids from entering the secured area of the airport from the outside. However, passengers may pack liquids and gels into their checked baggage. To aid with confusion on what passengers can and cannot bring into the cabin via carry-on items, the TSA has come up with a program called "3-1-1." Travelers may pack liquids and gels in their carry-on luggage provided they pack them in 3.4-oz. containers, all of which can fit into a quart-size plastic bag. Passengers need to place this bag into one security bin for screening at the checkpoint.
TSA officers screen every piece of luggage before it boards an aircraft. Though most bags undergo an X-ray, some bags may require opening for further inspection. For this reason, the TSA doesn't usually permit the use of baggage locks on checked bags. Should a locked bag require inspection, the TSA will cut the lock to gain access to the bag. Alternatively, the TSA has worked with several baggage lock companies to create a lock that TSA officers can open with a universal key; the TSA permits these locks. When purchasing baggage locks, look for a red diamond on the packaging to indicate that it is airport security safe.
Whether passengers plan to check their luggage or bring it on board as a carry-on, certain items aren't permitted on an aircraft under any circumstances. For safety and security reasons, the TSA does not permit spray paint, strike-anywhere matches, fire extinguishers, chlorine, lighter fluid, fireworks or gun powder. In addition, passengers can pack liquids and gels in excess of 3.4 oz. in checked bags but cannot bring them through security in a carry-on bag. Somewhat surprisingly, the only item not permitted in a checked bag but allowed on board in a carry-on is an everyday cigarette lighter.
