Hi Evelyn, You can't control how many times, and where your checked luggage may be checked. Even if they check it in your presence, they can check it again at any point between where you leave it, and when it reaches the belly of the aircraft. If at any point, they can't gain entry, they can break the locks in order to gain entry. The locks do keep luggage from accidentally opening, but they are no protection against anyone who really wants to open the bag. For instance, if you have a hard sided Sampsonite bag, any key from a similar bag will open it.
Andy
