For those of you not from the US, the TSA, or transportation safety administration, sets all guidelines and regulations for commercial air transit. Here, you are allowed to lock your baggage, but under average circumstances, you can only use TSA approved locks which use one of 7 keys which TSA officers keep on them. These 7 keys were adopted based on the most overwhelmingly common locks used on luggage prior to the creation of the TSA. The idea is that the TSA can open any luggage, but other people cannot open your bags. That's all well and good, but if you can buy the locks or worse, find images of the keys online, you could reverse engineer the keys. As it turns out, people all over the internet have done exactly that.
You can find the files on github and they work surprisingly well. This may be worrying to you, and rightfully so. Anyone with these keys can open your luggage. What can you do to prevent this? Well there is one circumstance where you must use a lock that isn't TSA approved. If you are flying with a firearm you are required to lock it in a method the TSA keys cannot open it. What if you don't want or don't have a gun? That is no big deal, just pick up a signal flare pistol. You can find them for around $20 and if they don't even work, it doesn't matter. Declare it and follow the procedure at your airport or airline. They are 50 states legal and can be used to keep sensitive luggage safe.