Have you ever wondered how those little boxes that you tap your card to open doors work? What are they reading on the card? How do they ultimately unlock the door? And, are they even secure? In this talk, we will answer all of those questions and more. We will walk through how access-control systems, in general, work, and dig into the details of the most popular systems. Fortunately for the entertainment value of this talk, there be dragons in our doors. We will walk through some of the most high-profile attacks in detail and then dive into some more fundamental flaws with how the systems are designed. All of these discussions will be accompanied with live demos and first hand experience. After this talk, you will look at the world, especially doors, differently -- weaknesses everywhere! My hope is that we can all learn from past mistakes and create a more secure and less frustrating tomorrow together