Cody Brocious demonstrated that How a simple Dry erase marker allows him to open an Onity hotel room door lock with an Arduino, which is totally James Bond. Brocious created a proof-of-concept device to show to security experts and press. The company responsible for the popular locks, Onity, has promised that it is going to find a fix to this exploit. In order to build and test all of this yourself you will need the following: A DC barrel jack, 5mm outer diameter, 2.1mm inner diameter and 5.6k resistor.
Source: https://thehackernews.com/2012/10/four-million-hotel-locks-vulnerable-to.html