Absent a federal privacy law in the U.S., creative plaintiffs’ lawyers have filled the void by filing hundreds of lawsuits each year alleging novel state law theories to challenge the collection of information on the internet. The most active bench of privacy advocates has seized on the California Invasion of Privacy Act (CIPA) to file a barrage of privacy litigation based on a decades-old law. The latest filings have focused on the argument that commonplace tracking software, like cookies or pixels, constitutes “pen register” and “trap and trace” devices that may not be used without consent or a court order. In this guest article, Blank Rome partner Rachel Schaller laid out plaintiffs’ pen register litigation playbook and provided strategies to defeat CIPA claims.