How do I remove a knogo wafer?

I received a pair of pants from goodwill and I noticed that there was one of those electronic devices on it that stops people from stealing it. I dont want to take the pair of pants into a store and ask somebody to remove it for me because I know they would probably mark me as a theif or something, but that isn't the case at all. I was wondering if there was any trick to removing one without damaging the pants or anything. Thanks :)