They kinda breezed through that part of the show. Binary code uses a ones and zeros organized in particular ways to represent different numbers/letters. Basically like the dots and dashes in morse code. I'm not sure if theirs was actually "binary code", cause I can never remember how to assign the values, or just using zeros and ones to be appear binary code-like. Devin had to memorize the 4 sets of 1s and 0s that each corresponded to a particular number between 0 and 9, I think, decode that at his first stop, and then enter that final number at his second stop. Honestly, it was pretty impressive that he was able to do it in one shot; I'm good at memorizing things when they're all different, but all those ones and zeros would have tripped me up.