Airport security is easiest when travelers stop thinking of it as one universal checklist. The broad goals are similar worldwide, but the details can change by country, airport, screening equipment, and even the terminal used for a connecting flight. A bottle that is acceptable at one checkpoint may be rejected at another, while laptops may stay inside a bag in one lane and need to come out in the next.
The safest approach is to check the rules for every airport on the itinerary before packing. That includes the departure point, connecting airports, and the airport used for the return trip.
Liquids Are Still the Rule Most Likely to Cause Trouble
The familiar 100-milliliter limit remains the safest standard to pack around. In the United States, carry-on liquids, aerosols, gels, creams, and pastes generally must be in containers of 3.4 ounces, or 100 milliliters, or less and fit inside one quart-size clear bag. European Union rules likewise generally restrict individual containers to 100 milliliters inside a transparent one-liter resealable bag.
The United Kingdom is more variable because some airports with newer screening equipment permit larger liquid containers, while many still use the 100-milliliter limit. Travelers should not assume that a rule used on the outbound flight will apply on the way home.
Container size matters, not the amount left inside. A half-empty 200-milliliter shampoo bottle can still fail a checkpoint operating under a 100-milliliter limit.
Medicines, baby milk, baby food, and liquids required for special diets commonly receive exemptions, although they may need separate screening. Keep them accessible and be ready to explain what they are.
Pack for the Checkpoint, Not Just the Cabin
Carry-on baggage is screened for security, not simply for size and weight. Knives, many sharp tools, certain sporting equipment, explosives, flammable substances, and realistic replica weapons can be prohibited from the cabin even when they seem harmless in ordinary use.
The important distinction is that “not allowed in carry-on” does not always mean “not allowed to travel.” Some items may be accepted in checked baggage if packed according to aviation and airline rules. Others are forbidden from aircraft entirely.
Before flying with an unusual object—camping equipment, tools, self-heating products, large aerosols, specialty batteries, or sports gear—check both the security authority and the airline. Airline restrictions can be stricter than the baseline aviation rule.
Power Banks and Spare Batteries Belong With You
Battery rules deserve special attention because they are safety rules as well as checkpoint rules. Spare lithium batteries and power banks should be carried in the cabin, not packed in checked luggage. Battery terminals should be protected from short circuits, and damaged or recalled batteries should not be taken aboard.
Capacity also matters. Most everyday rechargeable batteries up to 100 watt-hours fall within normal passenger limits. Larger batteries can require airline approval, and very high-capacity batteries may be prohibited on passenger aircraft.
If a carry-on bag is taken from you at the gate and checked into the hold, remove power banks and spare lithium batteries first. Do the same with e-cigarettes or vaping devices where applicable, since those devices are also generally restricted to the cabin.
Identification Rules Can Stop a Trip Before Screening Starts
Security identification requirements are separate from passport and immigration requirements. For international travel, a valid passport and any required visa or entry authorization remain essential even if a different form of ID would technically satisfy an airport checkpoint.
For U.S. domestic flights, adults using a state-issued driver’s license or identification card must now use a REAL ID-compliant version or present another accepted form of identification, such as a passport. Travelers without acceptable ID may face identity-verification procedures, additional screening, or denial of access to the checkpoint if identity cannot be confirmed.
Names on reservations should also match travel documents closely. A minor spelling error may be fixable, but relying on airport staff to solve a document mismatch is an unnecessary risk.
Electronics Procedures Depend on the Lane
Newer computed-tomography scanners can produce detailed three-dimensional images of cabin baggage, allowing some checkpoints to screen electronics and liquids without removing them. Other lanes still require laptops or other large electronics to be placed separately.
Follow the instructions at the checkpoint rather than copying what happened at the previous airport. Screening equipment can differ even within the same building.
In the United States, routine shoe removal at standard TSA checkpoints ended in July 2025, so most passengers can keep footwear on during screening. Additional screening can still be required when an alarm is triggered or an officer directs it.
Duty-Free Liquids Need Care During Connections
Buying a large bottle after security does not guarantee that it will survive a later checkpoint. Duty-free liquids may be allowed when sealed in an approved tamper-evident bag with proof of purchase, but transfer rules differ and additional screening can occur.
Do not open the sealed duty-free bag before reaching the final destination if a connection is involved. When changing countries or terminals, check whether the transfer requires passengers to clear security again.
A Faster Checkpoint Starts Before Leaving Home
Good security preparation is mostly about removing uncertainty. Keep liquids, medication, travel documents, and electronics easy to reach. Empty water bottles before screening. Remove forgotten knives, tools, loose ammunition, and other prohibited objects from backpacks that may have been used for work, hiking, or sports.
Most importantly, verify the official rules shortly before departure. Technology is changing quickly, but airport security is not becoming identical everywhere. Travelers who pack for the strictest checkpoint on their route are far less likely to lose an item, miss a connection, or start a trip with an avoidable delay.