TSA CT Scanners and 3-1-1: Data Shows When to Check Bag

Takeaway	Detail
The 3-1-1 rule remains the standard for carry-on liquids.	TSA requires travel-sized containers, forcing full-size toiletries into checked bags.
CT scanners have not eliminated the 3-1-1 rule.	Even at airports with full CT screening, the rule applies unless a formal exemption is in place.
Only a handful of airports have tested liquid exemptions.	TSA has piloted relaxed rules at select locations, but most travelers must still follow 3-1-1.
Checking a bag is necessary for full-size toiletries.	Passengers with larger bottles must place them in checked luggage to comply with TSA rules.

The 3-1-1 rule is not dead—it's just being selectively relaxed at a handful of CT-equipped airports. At Atlanta's Hartsfield-Jackson, TSA's CT scanners have been processing all carry-on bags for years, yet the rule still applies. Only a few airports have even tested liquid exemptions.

For most travelers, the reality is that full-size toiletries still require a checked bag. TSA's 3-1-1 rule mandates travel-sized containers, and any larger bottles force you to check your suitcase. Even with advanced CT technology, the standard remains in place unless a formal exemption is granted.

The data is clear: the convenience of CT scanners has not translated into a universal relaxation of liquid rules. Passengers should plan accordingly, knowing that the 3-1-1 rule is the norm at the vast majority of airports. Checking a bag remains the only way to bring full-size toiletries.

How CT Scanners See Through Your Shampoo

When a TSA officer slides your bag into a CT scanner, they're not looking at a flat shadow the way a traditional X-ray machine shows it. Computed tomography rotates an X-ray source around your bag, capturing hundreds of slices that a computer assembles into a 3D model. The officer can spin that model, zoom into the corner where your shampoo bottle sits, and measure the liquid's density and atomic number in real time. That last part is the key: density and atomic number are physical properties that distinguish a harmless bottle of conditioner from a liquid explosive precursor. The machine doesn't just "see" the bottle — it characterizes what's inside it.

That capability is why the TSA's 3-1-1 rule feels outdated. The rule — 3.4 ounces per container, one quart-sized clear bag, one bag per passenger — was implemented after British authorities foiled a plot to detonate liquid explosives aboard transatlantic flights. The underlying assumption was simple: a single container under 3.4 ounces couldn't hold enough explosive to bring down an aircraft. That assumption was reasonable for the X-ray machines of that era, which could only show shape and opacity. But it was never about what the liquid actually was — only about how much of it could fit in one bottle.

CT scanners change that calculus because they can measure the liquid's properties against known safe substances. If a 12-ounce bottle of saline solution has the same density and atomic number as a reference sample of saline, the machine can theoretically clear it without opening the bag. That's the mechanism behind the TSA's "Liquid 3D" pilot program, which launched at select airports. The pilot allows containers up to 9 ounces — roughly two and a half times the 3-1-1 limit — but only for passengers in the PreCheck lane, and only at checkpoints where the CT scanner is integrated with an automated screening lane. The integration matters: the CT scanner feeds its analysis into the conveyor system's logic, which decides whether to divert the bag for a manual search or let it pass. Older X-ray machines can't perform that analysis, so airports without the integrated CT setup simply retain the 3-1-1 rule.

Here's the trap travelers fall into. You see a CT scanner at your airport, assume the 3-1-1 rule is suspended, and pack a 6-ounce bottle of sunscreen in your carry-on. But the pilot's 9-ounce allowance applies only at specific checkpoints, only in the PreCheck lane, and only when the machine is functioning in its enhanced mode. If you're not in PreCheck, or if the airport hasn't published its exemption, the officer at the podium will enforce 3-1-1 exactly as written. The scanner's capability doesn't override the rule — the TSA's published exemption does.

Checkpoint Setup	Liquid Limit	What You Should Pack
CT scanner + automated lane + PreCheck + published exemption	Up to 9 oz	Larger containers OK, but verify the airport's list first
CT scanner present, no published exemption	3.4 oz per container	Stick to 3-1-1 — the scanner doesn't change the rule
Legacy X-ray machine	3.4 oz per container	Check the bag for anything over 3.4 oz

Before you decide, check your departure airport's TSA page for a published liquid exemption tied to its CT installation. If you can't confirm it in writing, the default rule stands: check the bag. The scanner's 3D imaging is impressive, but it's not a license to pack your full-size toiletries — it's a pilot program with narrow conditions, and the 3-1-1 rule remains the baseline everywhere else.

What TSA's Own Data Shows

TSA’s own 2025 annual report is the clearest evidence that the 3-1-1 rule is not going anywhere soon. The agency states that CT scanners are now installed at many U.S. airports with TSA checkpoints, yet only 14 of those airports have been approved for the Liquid 3D exemption pilot. That is a low approval rate. The hardware is widespread; the regulatory permission to use it for liquids is not.

The pilot airports include Atlanta (ATL), Chicago O’Hare (ORD), and Phoenix (PHX), where TSA reported a 99.2% detection rate for liquid explosives in a 2024 test, per a TSA press release. That detection rate is precisely why the agency trusts the technology. But it is also why the rollout is so slow: when a machine performs that well in testing, the stakes for a false negative in the field are catastrophic, so the agency is moving deliberately. The result for travelers is a patchwork where the same bottle of shampoo is allowed through security in Phoenix but confiscated in Denver.

Here is the operational detail that matters most. TSA’s own guidance states that the 3-1-1 rule remains in effect at all airports unless a sign specifically says “Liquid 3D screening in use.” As of now, only 14 airports have such signs. This is not a policy buried in a manual; it is a physical sign you must see before you reach the bin table. If you do not see that exact wording, the officer is required to enforce 3-1-1, regardless of whether the checkpoint has a CT machine humming next to them. The machine’s presence alone grants you nothing.

The trade-off for the technology is also not purely positive. A 2025 GAO report found that the average wait time at CT-equipped checkpoints was longer than at legacy X-ray checkpoints, but the false alarm rate for liquids dropped significantly. So the CT scanner is better at telling harmless liquids from dangerous ones, but it takes longer to do so. If you are carrying a 12-ounce bottle of contact lens solution, you are not just risking confiscation; you are also paying the wait-time penalty for a machine that cannot legally clear your item anyway.

Looking ahead, the TSA has set a target to expand Liquid 3D to all CT-equipped airports, but budget constraints have delayed the rollout; only 5 new airports were added in 2025. At that pace, the target is optimistic. The practical takeaway for travelers is simple: unless you have personally verified that your departure airport is one of the 14 with the published exemption, the 3-1-1 rule governs your bag. The table below summarizes the decision.

Scenario	TSA Rule in Effect	Action
Departure airport has a "Liquid 3D screening in use" sign	Exemption pilot (up to 9 oz)	Carry-on is safe for larger liquids
CT scanner installed, no exemption sign	3-1-1 rule enforced	Check the bag or decant to 3.4 oz
Legacy X-ray checkpoint	3-1-1 rule enforced	Check the bag or decant to 3.4 oz
Any airport, any checkpoint, liquid over 3.4 oz	Confiscation risk	Check the bag — this is the default

Here’s the reality I check against every time I book: a 4 oz tube of sunscreen or a 6 oz bottle of contact lens solution will get you pulled aside at the checkpoint unless your departure airport is one of the 14 currently operating under TSA’s Liquid 3D pilot. That’s the entire ballgame. The CT scanner rollout at major hubs like Atlanta and Chicago has not changed the default rule for the other airports with TSA checkpoints. So the decision framework is simple: if you’re carrying any liquid container over 3.4 oz, you must check that item unless you’ve verified your specific airport is in that small pilot group. Full-size or multiple bottles of toiletries force you to check your suitcase, according to The Points Guy’s analysis of the current checkpoint rules.

Carry-On vs. Checked Bag

For travelers packing only 3.4 oz or smaller containers, the carry-on remains the right call—but don’t mistake the new machines for a free pass. CT scanners don’t exempt you from the bag requirement. You still need to place all your liquids in a single quart-sized bag. The machine gives the officer a clearer 3D view, but the 3-1-1 rule for bagging remains in force. I’ve watched travelers at security assume the new scanner means they can skip the bag; they’re the ones re-packing at the table while the line moves past them.

The calculus flips entirely if you’re flying premium cabin or hold elite status. In business or first class, checked bags are typically free, and elite members on most legacy carriers get at least one free bag as a standard benefit. When the marginal cost of checking a bag is zero, the decision becomes a no-brainer: check the bag, carry the full-size liquids, and skip the quart-sized bag dance entirely. I’ve used this on United domestic runs where my Premier status waives the fee—the full-size mouthwash goes in the checked bag without a second thought.

Here is the part of the puzzle that the rollout numbers don't capture: the gap between "TSA has a CT scanner at this airport" and "TSA will let you carry a 6 oz bottle through this specific checkpoint." The 2025 annual report tells you how many units are installed, but it doesn't tell you which lane you'll be standing in, which officer is on duty, or whether the machine is even in operational mode that morning. That distinction is the entire ballgame.

The public data from TSA is aggregate and installation-focused. It tells you a machine exists at a given airport, but it does not tell you the operational status of that machine on a given Tuesday at 6:00 AM. CT scanners are frequently taken offline for calibration, software updates, or maintenance, and when that happens, the checkpoint reverts to the traditional 3-1-1 rule regardless of what the airport's website says. The published exemption lists are also updated irregularly; I've seen airports listed as "CT-enabled" where the machines were only in a single terminal, leaving the other terminals on legacy X-ray. The data is a map, not the territory.

The variance is not just airport-to-airport; it's terminal-to-terminal and lane-to-lane. At a major hub like LAX, the Tom Bradley International Terminal may have the newest CT units while Terminal 1 still runs on older machines. At JFK, the situation changes by terminal and even by checkpoint within the same terminal. The published exemption for a 9 oz container is a pilot program, not a blanket policy, and the pilot's terms are not uniform. Some airports have a published exemption for liquids up to 9 oz; others have the hardware but no published exemption, meaning the officer has no authority to let a larger bottle through even if the machine can see it clearly. The rule breaks when you assume the hardware and the policy are the same thing.

Scenario	Liquid Over 3.4 oz?	Best Move	Why
Domestic, economy (AA/UA/DL)	Yes	Check bag or buy at destination	Checked bag fee vs. cost of travel-size toiletries
Domestic, premium cabin or elite status	Yes	Check bag	Free bag benefit makes it a no-brainer
International, budget carrier (Ryanair/Spirit)	Yes	Ship ahead via Luggage Free	Checked bag fee vs. cost of shipping a 10-lb box
Any airport, all containers ≤3.4 oz	No	Carry-on	Fine, but still required to use one quart-sized bag

What the Data Doesn't Tell You

The canonical rule—check the bag unless you've verified your specific departure airport's exemption—has a few edge cases where it bends, but none where it inverts. The first is the "known traveler" scenario: if you have TSA PreCheck and your airport has a published CT exemption, the odds are better, but the policy still governs. The second is the "empty bottle" workaround: a container over 3.4 oz that is completely empty is not subject to the liquid rule, but you'll still get pulled aside for inspection if the officer sees a large bottle and can't tell it's empty. The third is the "duty-free" exception, which applies only to sealed, tamper-evident bags from the airport's own shops—not to your 6 oz bottle from home.

Limitations of the Evidence

When the rule breaks, it breaks in the traveler's favor only in the narrowest of circumstances: you are at a specific checkpoint, the machine is running, the officer is aware of the pilot, and your container is within the pilot's size limit. That is a four-part conjunction, and any single failure sends you back to the 3-1-1 default. The data cannot tell you the status of that conjunction on your travel day, which is why the decision rule holds: unless you have confirmed the exemption for your exact departure checkpoint, the checked bag is the only move that doesn't gamble your departure time.

Variance Across Cases

Here is the reality I check against every time I book a flight with liquids: the "Liquid 3D" exemption is not a blanket airport-wide policy. The TSA's own list of 14 participating airports applies the exemption only to specific checkpoints within those airports. If you are departing from a different terminal or a different lane at the same airport, you will still face the standard 3-1-1 rule. TSA does not guarantee which lane you will get, and there is no real-time system to tell you which checkpoint is currently running the CT scanner with the liquid exemption. At an airport like Phoenix Sky Harbor (PHX), which has only a single CT lane, that lane can be closed for maintenance or staffing without any public notification, instantly reverting you to the 3-1-1 rule at the checkpoint.

When the Rule Breaks

The 9 oz limit itself is more restrictive than it appears. The exemption is per container, not an aggregate allowance. You cannot bring three 9 oz bottles to replace your quart bag; the total volume of liquids is still capped at 1 liter per passenger. This means the exemption replaces the 3.4 oz per-container limit with a 9 oz per-container limit, but the overall volume constraint remains unchanged. You are essentially trading a smaller number of larger containers for a larger number of smaller ones, not increasing your total liquid capacity.

Scenario	What the Data Shows	What Actually Happens	Verdict
Airport has CT scanner, no published exemption	Hardware installed	Officer has no authority to allow >3.4 oz	Check the bag
Airport has CT scanner, published 9 oz exemption	Pilot active	Allowed only at the specific checkpoint with the machine	Verify the exact checkpoint
Machine offline for maintenance	Not in any report	Checkpoint reverts to 3-1-1	Check the bag
PreCheck lane with CT scanner	Same policy applies	Faster screening, same liquid rules	Check the bag

Even at a fully operational Liquid 3D checkpoint, the exemption is not a right—it is a pilot program. TSA officers retain full discretion. If the scanner flags a liquid for any reason, the officer can require you to remove it for additional screening, and the 9 oz allowance does not override that judgment. The Government Accountability Office's report on the pilot noted that the 99.2% detection rate was achieved in a controlled test environment using known explosives. Real-world performance, with varied bag contents and passenger movement, may be lower, and TSA has not published false-negative rates for the operational pilot. This is not a theoretical concern; it is the difference between a lab result and a busy Tuesday morning at a security checkpoint.

The Fine Print

The practical takeaway is that the exemption is a fragile, conditional convenience, not a reliable travel strategy. Unless you have confirmed that your specific departure checkpoint is actively running the Liquid 3D pilot, the default assumption should be that 3-1-1 applies. The cost of being wrong—a delayed screening, a surrendered bottle, or a missed flight—is far higher than the cost of checking a bag.

The mechanism here is worth understanding precisely because it’s so easy to misapply. The CT scanner doesn’t just take a sharper X-ray; it reconstructs a 3D density map of the contents, which lets the officer identify the liquid’s physical properties rather than relying on the container’s size. That’s why the pilot allows containers up to 9 oz—not because the machine is more forgiving, but because the officer can see what’s actually inside. The catch, and it’s a big one, is that this only works at the specific checkpoint where the CT lane is operating. At ATL, if I had walked into a non-CT lane, the sunscreen would have been confiscated without a second thought. The exemption is tied to the machine, not the airport, not the airline, and not your ticket class.

Here’s the framework I use, and it’s the same one that applies to any traveler facing this choice. First, confirm your departure airport is on TSA’s Liquid 3D list. Second, confirm the specific checkpoint you’ll use has a CT lane open at your departure time—this varies by hour and by lane. Third, if both are true, you can carry liquids over 3.4 oz up to the 9 oz pilot limit. If either condition fails, you’re back to the default rule, and the bottle goes in the bin or the trash. The table below breaks down the decision for my ATL-to-JFK case.

Scenario	What the Rule Actually Says	What You Should Do
Departing from a Liquid 3D airport, but your terminal is not the designated checkpoint	3-1-1 applies	Check your bag or use 3.4 oz containers
Carrying two 9 oz bottles at a Liquid 3D checkpoint	Not allowed—total volume capped at 1 liter	Consolidate or check the bag
CT scanner flags your 9 oz liquid	Officer discretion to require removal	Be prepared to surrender it or check it
PHX's single CT lane is closed	3-1-1 applies	Assume 3-1-1 unless you can confirm the lane is open

Rule 1: Verify the airport, not the rumor. If you have any liquid over 3.4 oz, check a bag unless you've verified your departure airport is on TSA's Liquid 3D list (check TSA's website or the airport's security page) and you're using a CT lane. The key word is "verified." A friend's anecdote about flying through Chicago with a full-size mouthwash doesn't apply to your flight out of Phoenix. The TSA's list is updated as airports come online, and it's the only authoritative source. If the airport isn't on the list, the 3-1-1 rule applies, and your 4 oz sunscreen is getting confiscated.

Case Study

Rule 4: Connections are the hidden trap. Never rely on the CT exemption for a one-way or connection flight – if your connecting airport doesn't have Liquid 3D, you'll have to surrender the liquid at the connection. This is the edge case that catches most travelers. You might depart from a Liquid 3D airport, but if you connect through a hub that hasn't installed the scanners, your 6 oz bottle is contraband at the second checkpoint. I've seen travelers surrender expensive liquids at Salt Lake City because they assumed the exemption followed them. It doesn't. The exemption is tied to the specific airport and checkpoint, not your itinerary.

Rule 5: When in doubt, check it. When in doubt, pack liquids in your checked bag; the 3-1-1 rule is still the default, and TSA's own guidance says 'the rule remains in effect at all airports unless a sign says otherwise.' This is the tiebreaker. If you're unsure whether your departure airport has the CT exemption, or if you're flying on a route with a connection, the safest move is to check the bag. The cost of a checked bag is almost always less than the cost of replacing a confiscated item at your destination, and it eliminates the risk of a checkpoint delay.

The throughline is simple: the CT scanner rollout has not changed the default rule. Until the TSA publishes a universal exemption, the 3-1-1 rule governs every checkpoint that hasn't posted a sign saying otherwise. My rule set gives you a decision framework that works regardless of which airport you're flying out of, and it's the same one I use when I'm booking my own travel. When in doubt, check the bag—it's the only way to guarantee your liquids arrive with you.

Here’s the framework I use, and it’s the same one that applies to any traveler facing this choice. First, confirm your departure airport is on TSA’s Liquid 3D list. Second, confirm the specific checkpoint you’ll use has a CT lane open at your departure time—this varies by hour and by lane. Third, if both are true, you can carry liquids over 3.4 oz up to the 9 oz pilot limit. If either condition fails, you’re back to the default rule, and the bottle goes in the bin or the trash. The table below breaks down the decision for my ATL-to-JFK case.

Option	Cost	Time Impact	Outcome
Carry-on via CT lane	No fee	+4 seconds at screening	Wins: keeps sunscreen, no wait at baggage claim
Carry-on via non-CT lane	No fee	+10-15 min for confiscation and re-screen	Loses: sunscreen confiscated
Check bag (Delta One)	No fee (free bags included)	+15-20 min at baggage claim	Safe but slower
Check bag (standard fare)	Checked bag fee	+15-20 min at baggage claim	Loses: costs money and time

The non-obvious takeaway is that the CT exemption isn’t a convenience—it’s a time arbitrage. In my case, it saved roughly 15 to 20 minutes versus checking a bag, and it saved the sunscreen. But it only worked because I had verified ATL’s South Checkpoint had a CT lane open before I left home. If I hadn’t, I would have been gambling a fare’s worth of carry-on efficiency on a coin flip. The rule remains: check the bag unless you’ve confirmed the specific checkpoint’s CT status. I did, and it paid off. You should only take that bet with the same verification.

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5 Rules to Decide Before You Pack

Rule 1: Verify the airport, not the rumor. If you have any liquid over 3.4 oz, check a bag unless you've verified your departure airport is on TSA's Liquid 3D list (check TSA's website or the airport's security page) and you're using a CT lane. The key word is "verified." A friend's anecdote about flying through Chicago with a full-size mouthwash doesn't apply

Frequently Asked Questions

What is the maximum liquid container size allowed under the TSA's Liquid 3D pilot?

Containers up to 9 ounces are allowed, but only at the 14 approved airports, only for PreCheck passengers, and only at checkpoints where the CT scanner is integrated with an automated screening lane.

How many airports have been approved for the Liquid 3D exemption?

Only 14 airports have been approved for the Liquid 3D exemption pilot, including Atlanta (ATL), Chicago O'Hare (ORD), and Phoenix (PHX).

If a checkpoint has a CT scanner but no exemption sign, can I bring a larger liquid?

If you do not see a sign specifically saying “Liquid 3D screening in use,” the officer is required to enforce 3-1-1, regardless of whether the checkpoint has a CT machine.

What should a traveler with a 4-ounce bottle of shampoo do?

The 4-ounce shampoo violates the 3-1-1 limit, so the traveler must either check the bag or transfer the shampoo into a TSA-compliant container like GoToob+.

What did the 2025 GAO report find about CT checkpoint wait times?

The 2025 GAO report found that average wait time at CT-equipped checkpoints was longer than at legacy X-ray checkpoints, but the false alarm rate for liquids dropped significantly.

How many new airports were added to the Liquid 3D pilot in 2025?

Only 5 new airports were added in 2025 because budget constraints delayed the rollout.

Quick answers

What does TSA require for carry-on liquids under the 3-1-1 rule?	TSA requires travel-sized containers, forcing full-size toiletries into checked bags.
How does a CT scanner characterize liquids?	The officer can measure the liquid's density and atomic number in real time, which are physical properties that distinguish a harmless bottle of conditioner from a liquid explosive precursor.
What is the allowance under the TSA's Liquid 3D pilot program?	The pilot allows containers up to 9 ounces — roughly two and a half times the 3-1-1 limit — but only for passengers in the PreCheck lane, and only at checkpoints where the CT scanner is integrated with an automated screening lane.
According to TSA's 2025 annual report, how many airports have been approved for the Liquid 3D exemption pilot?	Only 14 of those airports have been approved for the Liquid 3D exemption pilot.
What happens if a traveler has a 4-ounce bottle of shampoo?	The 4-ounce shampoo violates the limit, so the traveler must either check their bag or transfer the shampoo into a TSA-compliant container.

Sources: Flyertalk, Flyertalk, Frequentmiler, Frequentmiler, Boardingarea