Airport Security Screening: Everything You Need to Know

What Security Screening Is Checking For

Airport security screening exists to prevent weapons, explosives, and other prohibited items from being brought onto aircraft. The screening process is operated by different agencies depending on the country: the Transportation Security Administration (TSA) in the U.S., the Aviation Security (AVSEC) teams in Australia, contracted private operators at many European airports (under national authority oversight), and dedicated government agencies at most Asian hub airports.

The core technologies are X-ray screening for bags and luggage, walk-through metal detectors or millimeter-wave body scanners for passengers, and explosive trace detection (ETD) swabbing for targeted secondary checks. Most major airports now use computed tomography (CT) scanners for cabin baggage — these produce a 3D image, allowing officers to view items from multiple angles without physical inspection. CT scanners have been phased in at nearly all major U.S. airports since 2022.

The prohibited items list is extensive but the commonly misunderstood items are a short list: liquids over 100 ml, sharp objects (including multi-tools, pocket knives, and scissors with blades over 6 cm), self-defense sprays, firearms (these can be transported in checked baggage with advance airline and destination country notification), and power banks over 100 Wh. Firearms and lithium batteries are among the most frequently flagged items in checked bags, as they must be declared and meet specific packaging requirements.

The purpose of screening is not to confiscate items but to verify they are safe. A screener asking questions about a flagged item is routine — thousands of items are cleared daily after brief clarification. The process is not designed to be adversarial, and the vast majority of secondary bag checks are resolved within two to three minutes.

The 3-1-1 Liquids Rule

The 3-1-1 rule applies in the U.S. and forms the basis of liquids restrictions worldwide: containers must be 3.4 oz (100 ml) or smaller, all containers must fit into 1 quart-sized (approximately 1 liter) clear plastic bag, and each passenger is limited to 1 such bag. The bag must be presented separately at the checkpoint, placed flat on the X-ray conveyor. In practice, you can fit approximately 8 to 10 small containers in a standard quart bag.

Items that count as liquids under security rules include liquids, gels, aerosols, creams, and pastes. This means toothpaste, gel deodorant, peanut butter, hummus, yogurt, and liquid foundation are all subject to the rule — a fact that surprises many passengers. Snow globes, regardless of size, are also classified as liquids. Lipstick and solid deodorant are not liquid and can be packed normally.

Exceptions to the liquids rule exist for medically necessary liquids, baby formula and food, and breast milk in quantities exceeding 100 ml. These must be declared to the screener before screening and may require additional screening. Prescription medications are permitted in quantities "reasonably necessary for the duration of the trip" — keep medications in original packaging with your name on the label.

Starting in 2023, several EU airports began testing systems that allow liquids larger than 100 ml to pass through CT scanners without the bag requirement. Amsterdam Schiphol, London Heathrow, and several others had trials underway, though the rollout has been gradual and inconsistent. Always check current rules for your departure airport before assuming the 100 ml limit has been lifted.

Expedited Screening Programs

TSA PreCheck is the most widely adopted expedited screening program for U.S. travel. Approved members receive a "TSA Pre" indicator on their boarding pass and access dedicated lanes where shoes, belts, and jackets stay on, laptops and liquids remain in bags, and the queue is consistently shorter. The program costs $78 for five years (as of 2024) and the application involves an in-person appointment at an enrollment center where fingerprints and identity are verified.

Global Entry includes TSA PreCheck and adds expedited U.S. Customs processing for international arrivals. For frequent international travelers, it is the superior investment at $100 for five years. Enrollment involves an interview at a CBP Enrollment Center — major airports typically host these within the airport facility itself.

CLEAR is a biometric identity service that operates in U.S. airports and sports venues. Using fingerprints or iris scans to verify identity at the start of the security queue, CLEAR members skip the ID-check line and proceed directly to the X-ray conveyor. CLEAR does not replace TSA PreCheck screening — it only accelerates the identity verification step. The service costs $199/year (2024), though many credit cards and airline status programs offer free membership.

Outside the U.S., equivalent programs include the EU's Registered Traveller Program at participating airports, Australia's SmartGate Plus, and Japan's J-BIS enrolled traveler program. In the UK, Fast Track security passes are sold directly by airports including Heathrow and Manchester for a per-trip fee — typically £5 to £15 — giving access to dedicated security lanes regardless of ticket class.

What to Do at the Checkpoint

Preparation before reaching the conveyor belt is the single biggest factor in your screening time. Loosen your belt before reaching the belt. Move all loose change, keys, and metal items from pockets to your bag before joining the queue, not at the conveyor. Untie your shoes loosely so you can remove them in one motion. Have your liquids bag at the very top of your carry-on, accessible without rummaging.

At the conveyor, take one tray for your shoes, belt, and jacket. Place your laptop and liquids bag flat in a separate tray — many airports now require electronics larger than a mobile phone to be screened separately. Your carry-on bag goes in a third tray or directly on the belt. Avoid overstacking trays, which causes them to jam or tip.

If selected for additional screening — either the enhanced pat-down or explosive trace detection (ETD) swab of your hands and belongings — comply calmly. The ETD swab detects residue from a wide range of chemicals and is non-invasive. If you have recently handled firearms or fireworks, or been near certain industrial chemicals, mention this proactively to the officer. A pat-down is a standardized, documented procedure — you may request a private screening room and can have a companion present.

Prohibited items confiscated at the checkpoint are non-returnable in the U.S. In some countries — notably Japan and Canada — items can be placed in checked baggage if you have time to return to the check-in counter. If an item of significant value is flagged, ask the screener whether there is sufficient time to check it. TSA maintains a confiscated items program, but recovering items is rarely practical.

International Variations and Special Situations

Security procedures vary between countries. Israel's Ben Gurion Airport (TLV) is widely regarded as having the world's most thorough security protocols — passengers are interviewed by trained security officers before check-in, bags are inspected before being accepted, and the entire process can take two to three hours for some passenger profiles. Israel's approach is intelligence-led rather than purely technological, and it works: Ben Gurion has an outstanding security record despite being in a high-threat environment.

Japan's airports are known for thorough but extremely polite screening. Japan maintains separate security lanes for domestic and international flights and prohibits gel-type powerbanks (a rule unique to Japan). India's airports apply a double-screening model at most major international terminals: one checkpoint before check-in and a second at the gate, with a third random check sometimes applied at boarding.

Passengers traveling with special items should research in advance. Musical instruments are typically allowed as carry-ons if they fit in the overhead bin; cellos and larger instruments must be purchased a separate seat. Lithium batteries in power wheelchairs have specific watt-hour and approval requirements — contact the airline directly at least 48 hours before departure. Service animals have their own set of documentation requirements that differ by destination country.

Arrive at security with nothing in your pockets and your liquids bag accessible. PreCheck or its international equivalent pays for itself after just a few trips. If your bag is pulled for secondary screening, do not reach for it — wait for the officer to invite you to your items.