Black Hat hacker gains access to 4 million hotel rooms with Arduino microcontroller | ExtremeTech:

The best bit: By playing this 32-bit code back to the lock… it opens. According to Brocious, it takes just 200 milliseconds to read the sitecode and open the lock. “I plug it in, power it up, and the lock opens,” Brocious says. His current implementation doesn’t work with every lock, and he doesn’t intend to take his work any further, but his slides and research paper make it very clear that Onity locks, rather ironically, lack even the most basic security.