The best combination locks you can buy

Why you'll love it: If you're locking a bicycle out in the open and leaving it overnight, you want a lock that withstands cuts and other attacks. That's why the no-nonsense RockyMounts Shackleton U-lock is perfect.

Bike messengers the world over swear by U-locks because they are the most resistant type of lock during a sustained attack. Cable locks might be lighter, but they are generally easier to cut than the 12mm hardened steel shaft of the RockyMounts Shackleton.

There are stronger U-locks available, and I would recommend those if you are securing an expensive bike. But the Shackleton is the best combination U-lock: You get the convenience of a combination lock but with the strength of a U-lock.

Amazon purchasers loved the included mounting bracket that attaches to a bike. Others noted that the intimidating presence of a U-lock deters would-be thieves. This lock is not just for bikes: I have used it to lock a cooler in my truck bed when I am hiking and often use it to keep the sliding doors of my shed closed when I'm out of town. At under $20, it's worth keeping one around in case you ever need to beef up your security.

Pros: Sturdy, includes a bike mount

Cons: Not totally immune to strong bolt cutters

Buy the RockyMounts Shackleton on Amazon for $18.47

Why you'll love it: This Tarriss TSA Lock with SearchAlert is TSA approved, meaning you can keep everyone else out of your luggage without the TSA having to cut a lock for inspection.

If you want to keep thieves out of your luggage, it makes sense to lock it. But TSA regulation requires a bag to be unlocked if the owner isn't present; this is so that the TSA can get into it during inspection, if necessary. However, the agency allows the use of locks that are TSA approved, like the Tarriss TSA Lock with SearchAlert, which inspectors are able to unlock (usually with a special key).

With the Tarriss TSA Lock, not only can TSA agents inspect your luggage without damaging the lock, but you can also tell if it has been opened thanks to the SearchAlert function (a small indicator that turns from green to red).

Available as a two-pack, the three-digit combination should be easy to memorize and the flexible cable allows even fiddly zippers to be secured. Amazon buyers raved about the "crisp" rotation of the combination-lock wheels and the easily visible digits. TripSavvy called the lock its best overall.

At approximately $15 for two, the TSA lock is affordable for some peace of mind. It's a theft deterrent, but it isn't foolproof. The cable can be cut with strong cutters, and the three-digit combination is easier to crack than locks with more numbers. Some users report that the lock is easy to compromise without too much effort.

Pros: Lightweight, TSA approved, "opened" indicator

Cons: Users report that lock could be easily compromised

Buy the Tarriss TSA Lock with SearchAlert (2-pack) on Amazon for $15.97

Why you'll love it: A cable lock allows you to lock multiple items. The clear dial and distinctive look of the Knog Twisted Lock makes it our pick for the best combination cable lock.

Cable locks don't look as strong as their U-lock counterpart, but when you need to secure multiple things or awkwardly shaped objects, they are handy.

The Knog Twisted Lock has a 4.3-foot cable that lets you secure both the wheels and frame of a bike, or lock a kayak or cooler to an anchor pretty much anywhere. Knog uses a type of steel cable that makes the lock resistant to cutting. The four-digit combination makes it harder for others to guess. It is a great solution for locking something up for a short period of time and preventing grab-and-go theft. The silicone coating won't scratch bikes or things in your bag.

I found the numbers on the dials on this lock really easy to read, even when locking up a bike on a wet night. This is a vast improvement on some locks with chrome dials which reflect light, making the numbers illegible. I also appreciated the solid construction of the lock and positive feel of the dials as they clicked into place.

Pros: High-quality finish, long and flexible, four-number combination

Cons: Not the strongest lock you can buy

Buy the Knog Twisted Lock on Amazon for $24.95