Elevator hacking - 2 hour long walkthrough of elevator security and building security. So much fun in that one. Search for it on Youtube.
I recommend the full 2 hour version, with all the secrets: https://youtu.be/ZUvGfuLlZus
My second favourite talk: You spent all that money and your still got owned: https://youtu.be/tJsNu0VRKYY
I even watch these again and again.