Airport X-ray machines show the contents of your bag as a color-coded image that reveals what each item is made of. Security officers see every object inside your luggage, displayed in distinct colors that help them quickly identify whether something is organic material like food and clothing, metal like electronics and tools, or a potential threat. The same basic principle applies to body scanners, though those work differently than the machines your bags pass through.
What the Baggage Scanner Shows
When your carry-on slides through the tunnel-shaped scanner, X-ray beams pass through the bag from multiple angles. Dense materials absorb more of the beam, while lighter materials let more through. The machine translates these differences into a detailed, color-coded image on the officer’s monitor.
Three main colors appear on screen. Orange represents organic materials: clothing, food, paper, leather, and plastic explosives. Blue represents inorganic materials: metals, glass, and ceramics. Green indicates mixed materials that contain both organic and inorganic components, like certain electronics or composite items. Objects that are extremely dense, such as thick steel or lead, appear as solid dark shapes because the X-rays can’t penetrate them at all.
Modern baggage scanners use a dual-energy X-ray system, meaning they fire two different energy levels simultaneously. This lets the machine estimate the atomic composition of each object rather than just its density. A block of cheese and a block of plastic explosive might look similar on a basic density scan, but dual-energy imaging can distinguish between them because their atomic structures differ. That atomic-level analysis is what produces the color categories officers rely on.
How Newer CT Scanners Differ
Many airports are now replacing traditional 2-D X-ray machines with CT scanners for carry-on bags. These work like a medical CT scan: an X-ray camera spins around your bag and captures hundreds of images, then stitches them together into a 3-D view. Officers can rotate the image on screen and examine individual items from any angle without opening the bag.
The 3-D capability is a significant upgrade. Traditional scanners sometimes struggled with cluttered bags because overlapping items created confusing images. CT scanners can isolate objects in three dimensions and apply algorithms that automatically flag explosives, including liquid explosives, which older systems had difficulty detecting. This technology is also why some airports no longer require you to remove laptops or liquids from your bag. The scanner can see them clearly even when packed among other items.
What the Body Scanner Shows
The walk-through scanners you step into at the security checkpoint are not X-ray machines. In the United States, all airport body scanners use millimeter wave technology, which emits low-level radio waves rather than X-rays. Two antennas rotate around your body and capture the energy reflected off your skin and clothing to build an image.
What the officer actually sees is not an image of your body. The scanners use software called Automated Target Recognition, which replaces any image of your actual figure with a generic cartoon-like outline. If the scanner detects something unusual, like an object in your pocket or an item concealed under clothing, it highlights that area as a yellow box on the generic figure. The officer sees only where the anomaly is, not what you look like underneath your clothes. This software was specifically developed to address privacy concerns, and it eliminated the need for a separate officer viewing images in a remote room.
Medical Implants and False Alarms
If you have metal in your body, there’s a good chance the scanner will flag it. Joint replacements are the most common trigger. Patients with hip, knee, or shoulder replacements experience false alarm rates between 31% and 100%, depending on the type and size of the implant. Smaller hardware like screws, wires, or spinal implants triggers false alarms far less often, in the range of 0% to 40%.
Having multiple metal implants makes a flag significantly more likely. One study found that patients with more than one orthopedic implant were nearly six times more likely to trigger a false alarm. If this happens, you’ll typically receive a pat-down of the flagged area. The millimeter wave scanners themselves pose no risk to pacemakers, insulin pumps, or other electronic medical devices, since they use non-ionizing radio waves rather than X-rays or magnetic fields.
Radiation Exposure
The millimeter wave body scanners used in U.S. airports produce no ionizing radiation at all. They operate on the same part of the electromagnetic spectrum as radio waves, so stepping into one is comparable to standing near a Wi-Fi router.
For baggage scanners, the X-rays are contained inside the machine’s tunnel and shielded by lead-lined curtains at each end. You’re not exposed to any meaningful radiation from your bag being scanned. The older backscatter body scanners, which did use X-rays and were phased out of U.S. airports, exposed passengers to roughly 0.03 to 0.1 microsieverts per scan. That’s equivalent to about 3 to 9 minutes of the natural background radiation you absorb just by existing on Earth. A single dental X-ray delivers several times more. Those machines are no longer in use in the U.S., but you may still encounter them at airports in other countries.
What Officers Are Trained to Look For
Security officers aren’t examining every sock and sandwich in your bag. They’re scanning the color-coded image for specific patterns. Dense, dark objects that block the X-ray entirely get immediate attention because they could indicate something designed to be impenetrable to screening. Organic materials in unusual shapes or densities stand out because explosives register as orange on the display. Wires connected to unexpected objects raise flags because of their resemblance to detonation components.
If something looks suspicious, the officer will either ask to open your bag for a manual inspection or run it through the scanner a second time at a different angle. With CT-equipped checkpoints, the officer can digitally rotate the 3-D image and zoom into the suspicious area before deciding whether a physical search is necessary. The entire review typically takes just a few seconds for a normal bag, which is why the line keeps moving even though every single item is being analyzed.