Airport body scanners work by sending millimeter wave radio signals at your body, catching the reflections that bounce back, and using software to turn those reflections into a generic outline that flags anything unusual for a security officer to investigate. Nearly 950 of these machines are in service at roughly 340 U.S. airports, and every unit currently deployed uses millimeter wave technology rather than the X-ray-based scanners that were phased out over a decade ago.1Transportation Security Administration. Technology The scan takes about three seconds, produces no anatomical image, and you can decline it in favor of a pat-down.
What the Millimeter Waves Actually Do
The scanner operates in a band of the electromagnetic spectrum between 30 and 300 gigahertz, sitting just above the microwave frequencies used by cell phones and Wi-Fi routers.2Federal Communications Commission. Millimeter Wave 70/80/90 GHz Service At these frequencies, the radio energy passes through fabric but bounces off skin and denser materials. Inside the cylindrical enclosure, transmitters and receivers rotate rapidly around you, firing thousands of short pulses per second. Each pulse that reflects back is captured, and the system measures how long each return trip took.
That timing data is what makes the image possible. Skin has a much higher water content and density than clothing, so it produces a strong, consistent reflection. Anything tucked against the body, whether metal, ceramic, plastic explosive, or a thick wad of paper, disrupts the expected pattern. The scanner calculates the shape, position, and approximate density of whatever is causing the disruption, building a three-dimensional data set of the body’s surface and everything on it.3Pacific Northwest National Laboratory. Millimeter Wave Millimeter wave energy is non-ionizing, in the same broad category as radio waves from a cell tower.
What the Officer Sees on the Monitor
Raw scanner data never reaches a human eye. Every millimeter wave unit in U.S. airports runs Automated Target Recognition software that converts the three-dimensional scan into a simple, gender-neutral stick-figure outline on a nearby monitor. The software compares what it sees against a library of expected body shapes and known clothing signatures. When a reflection pattern doesn’t match skin or fabric, the system flags it with a yellow box on the corresponding area of the outline.
If nothing unusual is detected, the screen shows a green “OK” and you walk through. If the software flags a spot, it could be anything from a forgotten tissue in a pocket to a belt buckle that shifted during the scan. The officer sees only the generic outline with the highlighted zone, never an anatomical image.
Current units cannot store images. Manufacturers build them without any image-storage function, and the outline stays on the monitor only long enough for the officer to resolve any alarms before it clears automatically.4Department of Homeland Security. Privacy Impact Assessment Update for TSA Advanced Imaging Technology
What Happens When You Step Inside
You step into the enclosure and stand on two yellow footprints painted on the floor. The standard posture is arms raised above the head with elbows slightly bent, giving the rotating transmitters a clear path to your torso and the insides of your arms. You hold still for roughly three seconds.
A monitor facing the officer shows the result almost immediately. A clear screen means you’re free to exit. If a yellow box appears, the officer will ask you to step to the side and usually resolve the alarm with a brief pat-down of just the flagged area. That targeted check is different from the full-body pat-down you’d receive if you opted out of the scanner entirely.
TSA has modified its procedures for children 12 and under to reduce the likelihood they’ll need any pat-down. Officers consult with a parent or guardian about the best way to handle the screening and work to resolve alarms without additional physical contact when possible.5Transportation Security Administration. Will Children Receive a Pat-Down Screening? Standard screening procedures apply starting at age 13.
Your Right to Opt Out
You can decline the body scanner. Any passenger, including children, may opt out of Advanced Imaging Technology screening and receive a pat-down instead.6Senate Committee on Homeland Security and Governmental Affairs. TSA Airport Screening: Myth vs. Fact The pat-down is conducted by an officer of the same gender, and you can request that it be performed in a private area with a companion present. Opting out does not put you on any list or trigger additional scrutiny beyond the pat-down itself.
What you cannot do is refuse all screening. Federal regulations prohibit anyone from entering the sterile area of an airport or boarding an aircraft without submitting to screening.7eCFR. 49 CFR 1540.107 – Submission to Screening and Inspection Declining both the scanner and the pat-down means you won’t be flying that day.
How PreCheck Changes the Screening
If you have TSA PreCheck, the default screening at most checkpoints is a walk-through metal detector rather than the body scanner. PreCheck lanes are often set up without a scanner at all. You keep your shoes on, leave your laptop in your bag, and skip the arms-raised posture entirely.
The trade-off surfaces when you have a metal implant or medical device. If a walk-through metal detector would alarm on your implant, you can ask the officer to route you through the body scanner instead, which may let you keep your shoes on while still clearing the checkpoint.8Transportation Security Administration. I Am a TSA PreCheck Passenger and I Have a Metal Implant or Medical Device. What Should I Do? Passengers with pacemakers are advised not to go through walk-through metal detectors and should consult their physician before flying.
Medical Devices and Religious Head Coverings
If you wear an insulin pump, continuous glucose monitor, prosthetic, or other external medical device, tell the officer what it is and where it’s located before the screening starts. You can hand them a TSA Disability Notification Card or your own medical documentation, though presenting the card does not exempt you from screening.9Transportation Security Administration. TSA Disability Notification Card The card opens the conversation and lets you request alternate procedures, including a private screening area.
Check with your device manufacturer before flying about whether the device can safely pass through a body scanner, metal detector, or X-ray belt. Some manufacturers advise against exposure to certain screening technologies. If you cannot disconnect the device, it will undergo a visual and manual inspection performed gently around the area where it’s attached. You can ask for a Passenger Support Specialist at any point.10Transportation Security Administration. External Medical Devices
Religious and cultural head coverings, including hijabs, turbans, and yarmulkes, can stay on during the scan. If the scanner flags the area around the covering, an officer of the same gender will perform a targeted pat-down to resolve the alarm. If the alarm still can’t be cleared, you can ask to remove the covering in a private area rather than in view of the general checkpoint.11Transportation Security Administration. May I Keep Head Coverings and Other Religious, Cultural or Ceremonial Items On During Screening?
Is the Scan Safe?
The only body scanners still in U.S. airports emit non-ionizing radio waves. They do not produce X-rays, and they are regulated under the IEEE safety standard that governs human exposure to radio frequency fields between 3 kilohertz and 300 gigahertz.12U.S. Food and Drug Administration. Products for Security Screening of People The energy output is comparable to what you’d encounter standing near a cell phone or Wi-Fi router.
The older backscatter X-ray scanners, which did use ionizing radiation, were removed from all U.S. airports in 2013. Nothing you step into at a U.S. checkpoint today uses X-rays on your body.