Jobs and Woz built their own blue boxes which would emulate precise control tones to seize control of the phone system. They were inspired by this Esquire article from 1971 called Secrets of the Little Blue Box. The original creator of the Blue Box built his with failsafes in mind in case the law got too suspicious. Gizmodo ’79 is a week-long celebration of gadgets and geekdom 30 years ago, as the analog age gave way to the digital, and most of our favorite toys were just being born.”]
Source: https://gizmodo.com/phreaking-the-phones-before-there-was-hacking-5315755