Zappers are add-on programmes used by merchants with electronic cash registers to skim cash sales at the retail stage. Electronic cash registers may even be equipped with built-in and sophisticated skimming devices. In this article, the author discusses this phenomenon and presents the findings of the tax authorities in four of the many cases in which retailers use technology-based skimming devices. The author’s case studies show how important it is that the tax authorities regularly visit specific categories of retailers. There are also technological solutions to combat this sophisticated type of fraud.