I got this idea from a backpacking trip with Sheri. We were hiking through bear country, so I had her put a bear bell on her backpack. The tinkling of the bell was supposed to announce our presence to bears in the area. (I joked that it was the dinner bell for the bears!) That night, we were sitting around our little campfire when we heard the bell sound. I turned my light towards the sound just in time to see a raccoon dragging Sheri’s pack down the path. If not for that bell, we might not have known her pack was even gone.
The same bell can be used while traveling. Attach it to your bag and when you set it down in a cafe or on the train—be sure to secure it to a fixed object or join bags together with a locking carabiner—the bell will make a distinctive, yet unobtrusive sound if someone attempts to steal or rummage through it. As a side benefit, if you and your significant other get separated in a crowd, you can listen for the bell to find them. The bell also can be attached to the door knob of your hotel room.