I can tell you these things do work. I was crossing through Slovenia and Croatia this one time and they just happened to be fighting a war at the time. I don't rememebr exactly what town I was in, but the train was stopped and men armed with machine guns started searching the train. They made me open up my luggage and found a zip lock freezer bag that I had all my dirty laundry in. The guy was bugging me about it,"What is this. . Open it!" I told him no way, and that he could open it if he wanted to, but I would prefer if he did it in the hallway. After that they handed it back to me and left me alone.