The best luggage locks

Being clear about this changes which lock you buy and how much you spend. A lock on a zippered bag does four things, and three of them are worth the money.

1. It stops the bag opening by itself. A packed, expanded suitcase under a pile of other bags puts real load on a zipper, and a slider that walks backwards spills the contents into a baggage system. This is the most common thing a lock prevents and nobody markets it.
2. It deters the opportunist. Someone looking to unzip an outer pocket in a hotel luggage room or a train vestibule is choosing the easiest bag in the room. A lock moves you off that list in a second.
3. It tells you if the bag was opened - but only if it has an open-alert indicator. That is the whole argument for the feature.
4. It does not protect valuables. A coil zipper can be parted with a ballpoint pen and re-closed by running the sliders back over it, with the lock still shut. Treat the lock as a seal and keep anything you cannot replace in your personal item.

Which leads to the real rule: nothing irreplaceable goes in a checked bag, locked or not. What not to pack in checked luggage is the list, and it is shorter and stricter than most people expect.

Two certification systems exist, and either one is fine. Travel Sentry marks its locks with a red diamond; Travel Sentry describes its system as letting travelers lock a bag "so that their baggage or lock does not have to be forced opened and damaged during screening." Safe Skies uses a torch logo. Screening authorities that participate hold master keys for both.

• With a recognized lock: a screener who needs to hand-inspect your bag opens the lock with a master key, inspects, re-locks and leaves a Notice of Inspection inside. You get the bag back locked.
• Without one: TSA's own wording is that the lock "may have to be cut." It also states it is not liable for damage to locked bags opened for security purposes, so there is no claim to make afterwards.
• The mark has to be on the lock body. "TSA approved" in a listing title with no diamond or torch stamped on the metal is a claim, not a certification.

This is the only genuinely difficult choice on the page, and it is decided by your bag rather than by the lock.

If you own more than one kind of bag, buying one of each is cheaper than discovering at the airport that a shackle will not reach. Backpack users in particular should default to a cable - best travel backpacks covers which bags have lockable pulls at all, which is not all of them.

1. Two per checked bag. One on the main zipper, one on the expansion or secondary compartment. A bag with one lock and an unlocked expansion zipper is an unlocked bag.
2. None on a carry-on going through the checkpoint. If a screener wants it open you will be standing there, and a lock just slows the line. Lock it afterwards if the bag is going into an overhead on a long flight or into a luggage room.
3. Lock the pulls to each other, not to the bag. A pull locked to a fixed loop puts all the load on that loop and makes the bag harder to open legitimately.
4. Same combination on every lock you own. The failure mode here is not a thief guessing it - it is you forgetting which lock has which code at a baggage carousel.
5. Write the combination somewhere that is not the bag. A photo in your phone works. How to set a luggage lock covers the resetting procedure for both 3- and 4-dial types, including what to do when you have forgotten it.

• Key locks. A key is one more thing to lose mid-trip, and losing it means cutting your own lock off. There is no advantage over a set-your-own combination for luggage.
• Built-in locks you cannot change. Most good suitcases ship with an integrated TSA lock, which is fine and which you should use - but if the dials are fixed at 0-0-0 from the factory, reset them. An unreset built-in lock is the single most common open bag at a carousel.
• Non-TSA padlocks. Stronger, and that is exactly the problem: a screener who needs in will cut it and owes you nothing.
• Smart locks with an app and a battery. A luggage lock that needs charging and a phone adds two failure modes to a device whose entire job is to be trivially reliable.
• Strap-and-lock combinations get their own page, because the strap is doing most of the work - see best luggage straps for the ones with an integrated TSA lock.

Locks belong to the category of travel objects that are cheap, weigh nothing and either earn their place permanently or never come out of the bag. Best travel gadgets ranks eight of those by uses per trip, and the best travel steamers deals with the one that is most often bought and least often used.