On a sunny Saturday afternoon, the kind of temperate fall day that usually calls for a lounge in the park, high school seniors Jenny Li and Violet Killy were crouched over laptops in the fluorescent-lit library at Bronx High School of Science, writing code.

The two 17-year-olds were building an app to prevent snoozing MTA commuters from missing their subway stop. They had isolated the familiar ding-dong tones of the subway doors opening and closing, which the app would recognize and combine with acceleration data to track a subway rider’s trip.

“It’s a relatable problem we can solve for anyone who wants to take a power nap,” said Killy, who commutes to school from Manhattan.

Killy and Li were two of more than 4,000 students in 87 locations around the world who participated in Local Hack Day, a 12-hour student hackathon organized by Major League Hacking. Bronx Science was one of two hacking hubs in the Bronx, where educators and community organizations used the event to spark students’ interest in computer science.

“I think computer science has become a language of fluency,” said Eleanor Coufos, vice president of Bronx Science’s endowment fund. “You’re going to have to speak and work and collaborate with people who do use it.”

The prestigious Bronx Science—which has graduated multiple Nobel laureates—has a robust computer science program. About 10 percent of students currently pursue computer science/engineering at the school, and Coufos hopes that events like the hackathon will spur additional enrollment in coding classes.

Jack Cook, 15, is only a sophomore but has been to more than 20 collegiate hackathons in the past year, sometimes as far away as San Francisco, Dallas and Toronto. Cook proposed Bronx Science as a Local Hack Day host and helped plan the event.

Cook taught himself coding more than three years ago when he wanted to modify a video game. But it took a while to grasp the basics of the language before he could create something practical. Cook sees that delayed gratification as the major hurdle for students who are new to computer science.

“You’re writing code you might not see the value of at first,” he said.

Bronx-based computer science education organization Code/Interactive is helping low-income students warm up to coding through training programs at 20 high schools in New York City. The group hosted a Local Hack Day at Fordham Foundry, where close to 80 students piloted apps and websites.

“Coding and computer science will be pervasive in any industry that these kids end up in,” program director Tom O’Connell said.

O’Connell sees Code/Interactive as a critical force for convincing Bronx schools to commit to coding, in response to the Mayor’s announcement that all public schools will be required to offer computer science courses to all students within 10 years.

The non-profit is currently organizing Bronx teachers to implement one hour of coding instruction for students during Computer Science Education Week in December. Code/Interactive is also working with Borough President Ruben Diaz to convene Bronx principals for a conversation about computer science education before the end of the year.

“The Bronx is a hopeful borough because we’re the underdogs,” O’Connell said.

Omar Allen, 17, was one of about 80 students to participate in a Local Hack Day event at Fordham Foundry. Allen attends Fanny Lou Hamer Freedom High School in the Bronx, where 81 percent of students qualify for free lunch.

Allen learned some basic HTML and CSS during a coding class offered at NYU, and the hackathon—his first ever—provided another chance to build his skills. He worked with three other students to build the framework for an app and website called Stimul8, an anonymous social media site with self-help forums.

Allen was excited to find out that next year, Fanny Lou Hamer will offer AP Computer Science for the first time. He hadn’t thought about pursuing a career in programming before his first class, but Allen is reconsidering.

“This is a new path I could take,” he said.