I once had one of those darn sensors stuck to the bottom of my shoe while I was shopping at the mall. I set off the alarms coming and going everywhere I went. Finally, a security guard in Bloomingdale's told me to check the bottom of my shoes. I guess I wasn't the first person to have that happen.
Totally within the realm of possibilities b/c they have adhesive on one side. If the backing paper comes off, voila, it can stick to the bottom of your shoe, or even your clothes, your stuff...it's kind of a mess!