I was selling an item on Craig's list and wanted to be able to tell if the purchaser was giving me real or counterfeit cash. I asked for help and was immediately led over to the rack of counterfeit detector pens. I made my purchase and was on my way in a matter of minutes. Excellent customer service.
I usually purchase the pens that turn black when a bill is counterfeit. I purchased a 3 pack of pens that turn brown when conterfeit and one of my bills that turned dark yellow/brown was actually good but was brown. They were a little pricey as well.