I think the main purpose of the pens isn't to catch fakes once they are in the store, but to keep counterfeiters from even trying to use Target as a place to swap their fakes for real bills at all. My store was being hit pretty hard by counterfeiters for quite awhile. AP told me that there was (maybe still is) a pretty sophisticated counterfeit ring in our area. They would go to one Target, buy a few hundred dollars worth of merchandise, pay with fake cash and then take the items to another Target and return the stuff, getting real cash in return. Until we introduced the pens almost a year ago, we were receiving fake money about once a week on average (that we were aware of--I'm sure some of it slipped past us). Now that we have the pens, its only happened once that I've heard about.