11.1 AIT, WTMD, and Credential Authentication

11.1 AIT, WTMD, and Credential Authentication

Quick answer: TSA's Security Screening page uses millimeter-wave Advanced Imaging Technology (AIT) to screen for metallic and non-metallic threats under clothing without physical contact. AIT is non-ionizing radio-frequency energy in the millimeter spectrum. It does not use X-ray. Automated target recognition (ATR) software shows alarms on a generic outline identical for all passengers. The walk-through metal detector (WTMD) screens for metal. Credential Authentication Technology (CAT) authenticates the ID, the reservation, and Secure Flight status in near real time and can display TSA PreCheck® eligibility without a boarding pass. CAT does not eliminate airline check-in. Travelers still need a boarding pass at the gate.

This section is public passenger-screening technology for the TSO Assessment Battery (TAB) and the live checkpoint. It is not Sensitive Security Information (SSI). Do not invent unpublished alarm boxes, algorithm thresholds, or “secret” AIT opt-out percentages. Apply the published machine, the published clothing rule, and the published identity check.

AIT: what it does, and what it is not

AIT is the body scanner at the checkpoint. TSA states that millimeter-wave AIT safely screens passengers without physical contact for metallic and non-metallic threats, including weapons and explosives, that may be concealed under clothing. That is the operational split from WTMD: a ceramic blade, a non-metallic explosive, or another non-metal threat is not a WTMD problem. It is an AIT problem.

Safety. AIT meets national health and safety standards. The energy is non-ionizing radio-frequency in the millimeter spectrum, with no known adverse health effects. TSA's AIT FAQ adds that the energy emitted is 1,000 times less than international limits and guidelines. Candidates who call AIT an “X-ray booth” are describing the wrong physics. Checkpoint bag X-ray and CT are property systems. AIT is not X-ray.

Privacy. TSA uses automated target recognition software that eliminates passenger-specific images. The unit auto-detects potential threats and marks their location on a generic outline of a person. That outline is identical for all passengers. TSA's AIT process FAQ: if there is no alarm, an “OK” appears on the screen with no outline. There is no published public-facing “nude image” for the officer to interpret. The officer sees a cookie-cutter body map or an OK.

How the traveler uses it. TSA's process FAQ is short enough to memorize. The traveler removes all items from pockets, including non-metallic items, and walks into the imaging portal. Inside, the traveler stands in position and remains still for a few seconds while the technology creates an image in real time, then exits the opposite side and collects belongings. The entire process takes a matter of seconds. Empty pockets are not a courtesy. A phone, a tissue pack, a folded boarding pass, or a religious item left in a pocket is an alarm waiting to happen — and an alarm is a pat-down in the next section.

Who may decline AIT — and who may not

Generally, passengers undergoing screening may decline AIT in favor of physical screening (a pat-down). That is the public default. It is not a promise that every traveler can walk around the scanner.

Limited exception: some passengers must undergo AIT if their boarding pass indicates they have been selected for enhanced screening, in accordance with TSA regulations, before they arrive at the checkpoint. TSA says this occurs in a very limited number of circumstances. The vast majority of passengers are not affected. TSA's technology factsheet says the same thing in officer language: individuals selected for enhanced screening based on their boarding pass are not eligible to opt out of AIT. Do not invent a local “everyone can always refuse” rule. Read the boarding pass. Apply the published exception.

Secure Flight is why that boarding pass can differ from the person in front of you. Secure Flight identifies PreCheck-eligible travelers, people designated for enhanced screening (Selectee List), people who receive standard screening, and people who must be prevented from boarding (No Fly List and CDC Do Not Board List). CAT is how the officer sees that status at the podium.

Light outer garments, bulky clothing, and AIT eligibility

Any individual wearing a light outer garment or bulky clothing when screened through AIT is asked to divest it.

• A light outer garment is an outer layer with a full front zipper or buttons used to fasten the garment, excluding button shirts. Published examples: windbreakers, vests, suit/sport coats, blazers, and light jackets.
• Bulky clothing is a garment that is very loose or does not conform to the contour of the person. Published examples: oversize pullover hoodies, large sweaters, cardigans, and ponchos.

If the traveler cannot or is not willing to remove that layer, tell the officer — additional screening may occur. In a PreCheck lane, travelers typically keep light jackets for ordinary screening. If they request AIT, TSA Cares still requires removal of light jackets. PreCheck is not a coat-on AIT exception.

AIT eligibility is a physical test, not a preference. TSA Cares: the traveler must stand and walk unassisted for the duration of screening, and must stand shoulder width apart with arms above the head for five to seven seconds without support. If they cannot, they are not AIT-eligible. They receive a pat-down. Do not put a traveler who cannot hold the pose into the portal “to try.”

WTMD and CAT, including CAT-2

WTMD screens for metal. It does not replace AIT for non-metallic threats. TSA Cares is explicit for internal medical devices such as a pacemaker: the traveler should not be screened by the WTMD. Consult a physician before flying. If the traveler declines AIT or alarms the WTMD, the officer conducts a pat-down. Service animals typically go through the WTMD with the handler (together or separately on a leash). An alarm there is additional screening, including a pat-down.

CAT sits at the travel-document-checker podium, before AIT or WTMD. Adult passengers 18 and older must present acceptable identification. The officer asks for a photo ID. The traveler presents an acceptable physical or Digital ID into the CAT unit. CAT is linked to the Secure Flight database. It confirms travelers are ticketed for travel that day, improves fraudulent-ID detection, and displays the pre-screening status (such as PreCheck) the traveler is eligible for — all without a boarding pass. Two sentences candidates flatten:

1. CAT can show PreCheck eligibility without a boarding pass at the checkpoint podium.
2. CAT does not eliminate airline check-in. Passengers still need their boarding pass to show the airline at the gate.

CAT-2 adds optional facial comparison. TSA's Facial Comparison Technology factsheet: CAT-2 is deployed at about 350 airports. It helps officers verify that the person at the podium is the person on the credential, then direct the traveler to PreCheck, standard, or enhanced screening. Participation is voluntary. Travelers may decline the optional photo without recourse, keep their place in line, and receive an alternative ID check that does not use facial comparison. Travelers under 18 are not photographed. Photos are not stored after a positive match except in a limited testing environment. Facial comparison is not used for surveillance or a general law-enforcement watch. PreCheck Touchless ID is a separate enrolled-traveler program with participating airlines — not the default CAT-2 photo.

TSA PreCheck® is a risk-based lane, not a scanner brand. Typical PreCheck benefits: keep shoes, laptops, 3-1-1 liquids, belts, and light jackets. TSA still uses unpredictable security measures. No individual is guaranteed expedited screening. A PreCheck traveler can still walk through a WTMD, request AIT where available (jacket off), or receive a pat-down.

Realistic scenario: A traveler in a standard lane wears a blazer and an oversized hoodie, leaves a phone in a pocket, and says “I never go through the scanner.” The blazer is a light outer garment. The hoodie is bulky clothing. Both come off for AIT. The phone should have come out of the pocket. If the traveler declines AIT, that is generally allowed — unless the boarding pass shows enhanced screening, in which case AIT is required. A second traveler with a pacemaker should not use the WTMD; AIT or a pat-down is the public path. At the podium, CAT confirms the ID and shows PreCheck for a third traveler without needing the boarding pass there, then that traveler still keeps the boarding pass for the gate. The final decision rests with the TSA officer.