Refined hack opens locked hotel rooms… with a magic marker | extremetech.com

In late July, security researcher Cody Brocious demonstrated how an Arduino microcontroller and a bit of programming could be used to open the doors on some four million hotel rooms. For Onity, the company that manufactured the electronic lock, it was bad news — but not too bad. While Brocious exposed just how stupid-easy it was to open Onity-secured doors, the equipment he used wasn’t exactly inconspicuous.