Password, please ?

We're locking all cartoon channels on Astro to control the kids from watching too much TV. Besides, we're just starting to teach Amir to read. One day, Amir got hold of the remote and tried his luck to break the password to unlock those channels. After he had exhausted the three attempts, it prompted "Next try in 30 minutes". I wanted to laugh at what happen next. Amir entered "30" as the password repeatedly. Finally, he gave up and asked me, "Abah, TV kata use three zero. Apasal tak boleh ?". His mother teased him, "If you can read, you'll know that's not the password."

Banyak sangat nombor, mana satu untuk password ni ?