What TSA scanners actually see

TSA uses two main types of scanners at airport checkpoints: X-ray machines for bags and millimeter-wave scanners for your body. The X-ray machines work like the ones at a doctor's office—they send radiation through your bag and create a two-dimensional image on a screen that shows the density and shape of objects inside. A TSA officer watches this image in real time and can spot anything that looks suspicious: a knife, a battery pack, a full water bottle, or anything else that doesn't match what they expect to see.

The millimeter-wave body scanners you walk through use radio waves, not radiation. They bounce waves off your skin and clothing and create a detailed outline of your body. These scanners can detect objects hidden under clothes—metal and non-metal alike—but they cannot see inside your body or read personal information. If the scanner detects something, you'll be pulled aside for a pat-down or additional screening.

Both types of scanner send images to a monitor, and a real person—not artificial intelligence—decides whether what they see requires further inspection. The officer is trained to recognize the silhouettes of common items and to spot anything that breaks that pattern.

Key Takeaways

  • X-ray machines create a two-dimensional image of your bag's contents based on how dense each object is, allowing officers to see weapons, liquids, and electronics.
  • Millimeter-wave body scanners use radio waves to detect objects hidden under clothing without showing anatomical detail or reading personal data.
  • A trained TSA officer watches the scanner image in real time and decides whether an item needs closer inspection.
  • Scanners cannot see through solid objects like closed luggage or opaque containers, so officers may open your bag to verify what the X-ray showed.
  • Different items trigger different responses: some are confiscated, some require a pat-down, and some are straightforward cleared after visual confirmation.

How X-ray machines read your bag

When you place your carry-on on the conveyor belt, it travels through a tunnel where X-rays pass through it from one side. Different materials absorb different amounts of radiation. Metal absorbs a lot and appears bright white on the screen. Plastic, fabric, and paper absorb less and appear in shades of gray. Liquids and gels show up as darker areas. The machine creates a color-coded image: organic materials (food, paper, clothing) often appear in orange, inorganic materials (metal, glass) in blue, and mixed-density items in green.

The TSA officer watching the monitor can rotate the image, zoom in, and sometimes request a second scan from a different angle if something is unclear. If a laptop, a large battery, or a suspicious object appears in the image, the officer will ask you to remove it or will open your bag for a physical inspection. The X-ray cannot see through a closed suitcase or a sealed container, so the officer may need to look inside to confirm what the image showed.

Checked baggage goes through a different, more powerful X-ray system in the baggage handling area. These machines are designed to detect explosives and other threats. If something in your checked bag triggers an alert, TSA may open it, inspect the contents, and leave a notice inside.

How millimeter-wave body scanners work

The millimeter-wave scanner stands in a booth about the size of a phone booth. You step inside, raise your arms, and stand still for about three seconds. The machine emits radio waves in the millimeter range—frequencies between microwave and infrared—that bounce off your body and clothing. A receiver picks up the reflected waves and converts them into a detailed outline image that shows the contours of your body and anything on or under your clothes.

The image appears on a monitor as a generic human silhouette with highlighted areas where the scanner detected an object. The officer does not see your face, your genitals, or any anatomical detail—only a featureless outline with problem areas marked. If the scanner detects something, the officer will direct you to a secondary screening area for a pat-down or a hand-held metal detector scan.

Millimeter-wave scanners cannot detect items inside your body, and they do not store images. Once the scan is complete and cleared, the image is deleted. The technology is considered safe by the FDA and does not use ionizing radiation like X-rays do.

What happens when a scanner detects something

If an X-ray shows an item that concerns the officer—a lighter, a pocket knife, a full bottle of shampoo—you'll be asked to remove it or open your bag. Some items are confiscated (weapons, sharp objects, liquids over 3.4 ounces). Others are allowed but must be packed correctly (electronics must be accessible for inspection, batteries must be in carry-on, not checked). If the officer cannot clearly identify an object in the X-ray image, they will open your bag and ask you what it is.

If a millimeter-wave body scanner detects something, you'll be directed to a secondary screening area. A TSA officer will perform a pat-down of the area where the scanner detected an object. If you're wearing a belt, heavy jewelry, or have keys in your pocket, the pat-down may clear the alert. If the officer finds nothing, you're cleared to proceed. If they find a prohibited item, it will be confiscated.

You can request a pat-down instead of walking through a body scanner. Some travelers choose this option for personal or religious reasons. The pat-down takes longer but uses the same screening standard.

What scanners cannot detect

X-ray machines cannot see through solid, opaque containers. If your checked bag has a locked compartment or a sealed inner pocket, the X-ray will show a blank area, and TSA may open the bag to inspect it. Similarly, if you pack a book or a thick folder, the X-ray may not show what's inside the pages, so the officer may flip through it.

Millimeter-wave scanners cannot detect items inside your body or items completely hidden inside a sealed bag or container that you're carrying. They work only on what's on or when ready under your clothing. If you place a phone in your shoe, the scanner will not detect it because the shoe material blocks the radio waves.

Neither scanner can read the contents of a closed laptop, a sealed envelope, or a locked box. If the X-ray shows an opaque object, the officer will ask you to open it or will open it themselves during secondary screening.

Why TSA uses multiple scanning methods

TSA uses X-ray and millimeter-wave scanners together because each one catches different threats. X-ray machines are excellent at identifying metal objects and dense items like weapons or tools. Millimeter-wave scanners are better at detecting non-metal objects hidden under clothing, like ceramic knives or plastic explosives. By using both, TSA creates overlapping coverage that makes it harder for a prohibited item to slip through undetected.

Checked baggage screening also includes explosive-detection systems (EDS) that use computed tomography (CT) scanning—a more advanced form of X-ray that creates three-dimensional images. These machines are slower and more expensive than standard X-rays, so they're used only for checked bags, not carry-on screening at the checkpoint.

The combination of technology and human judgment is intentional. A machine can flag a suspicious shape, but only a trained officer can decide whether it's actually a threat or just an unusual lunch.

How to prepare for scanner screening

Remove your laptop, tablet, and large electronics from your carry-on before you reach the scanner. Place them in a separate bin so the X-ray officer can see them clearly without other items blocking the view. Remove your shoes, belt, and jacket, and place them in a bin. Empty your pockets completely—keys, coins, and phones should go in a bin or your carry-on.

Wear clothing without heavy metal (large buckles, metal zippers, underwire bras) if possible, because metal triggers the body scanner and leads to a pat-down. If you're wearing something with metal, let the officer know before you step into the scanner, and they can note it and skip the pat-down if the scan is otherwise clear.

Pack liquids in a clear, quart-sized bag and place it where you can easily remove it. Wrap sharp objects (razors, scissors) in cloth or plastic so they're visible on the X-ray but won't cut the officer's hand if they need to inspect your bag. If you're traveling with medications, keep them in their original labeled bottles—the X-ray officer will recognize them.

Frequently Asked Questions

Do TSA scanners use radiation?

X-ray machines use ionizing radiation, but the dose is very small—comparable to a few minutes of natural background radiation. Millimeter-wave body scanners use radio waves, not ionizing radiation, and are considered safe by the FDA. You receive more radiation from a cross-country flight than from a TSA X-ray scan.

Can TSA scanners see through my luggage?

X-ray machines can see through soft luggage and thin-walled bags, but not through solid, opaque compartments or locked sections. If the X-ray shows a blank area, TSA may open your bag to inspect it. Hard-sided luggage is more opaque, so some contents may not be visible on the X-ray.

What if the body scanner detects something but I'm not carrying anything?

False alarms happen. Metal in your clothing, a seam, a button, or even residue on your skin can trigger the scanner. You'll be directed to a pat-down, which will clear the alert if nothing is actually there. If you're concerned about false alarms, you can request a pat-down instead of using the body scanner.

Are TSA scanner images stored or shared?

Millimeter-wave body scanner images are deleted when ready after screening and are not stored. X-ray images of bags are not stored either—the officer sees them in real time on a monitor and they disappear once the bag passes through. Images are not shared with other agencies unless a prohibited item is found and a report is filed.

Can I refuse to go through a scanner?

You can request a pat-down instead of a body scanner. You cannot refuse all screening—if you decline both the scanner and the pat-down, you will not be allowed to board your flight. A pat-down takes longer but uses the same security standard and is a legitimate alternative screening method.