The TSA recommends using "TSA-recognized" locks if you choose to lock your luggage, but they do not strictly require it. The primary benefit of using a TSA-approved lock (which features a "Travel Sentry" red diamond logo) is that it allows security screeners to open your bag for inspection using a universal master key without damaging the lock or your suitcase. If you use a non-TSA-approved lock and your bag is flagged for a physical search, the TSA has the legal authority to cut or break the lock to gain entry, and they are not liable for the damage. While locking your bag provides a layer of protection against opportunistic theft and prevents the zippers from accidentally opening during transit, it is not a guarantee of total security. Many travelers prefer to use heavy-duty zip ties as a disposable alternative, as these also indicate if a bag has been tampered with. Ultimately, the TSA's priority is the ability to inspect any bag quickly; as long as you use a lock they can open with their specialized tools, locking your luggage is considered a best practice for peace of mind.