Indeed, Khan said she didn't know whether people would take the challenge seriously until she saw a video of a woman in Riyadh driving after midnight.
"The groups we have on Facebook, everybody who has been out has uploaded their videos so it's sort of an online relationship with everyone," she said.
Activists did not appeal for mass protests but urged Saudi women to begin a growing backlash against the male-only driving rules supported by clerics. Today's campaign came a month after single mother Manal Al Sheikh was jailed and held for a week after posting video of herself driving.
Her arrest turbocharged the cause fueled by Facebook and publicized on Twitter -- and was supported by some husbands
"We've seen men support their women and say, 'I want my woman, my wife to be independent and that's why I want her to drive,'" Quassemi said.
Protesters say the ultraconservative kingdom's gender apartheid is not just unjust but hideously inefficient. In one example, Saudi women working at a factory in Riyadh can drive lorries but not drive themselves home. And for low-income women, paying a driver up to $400 a month is a burden they cannot afford.
"It adds to that social injustice that women feel already in the Middle East," Quassemi said. "You know, if they can ride camels 1,400 years ago, why can't they drive cars today?"
As Saudi women push back, the optimists say that change is ahead. "Now that I've done it, I'm worried that now I won't be able to stop," Khan said.
The Associated Press contributed to this article.