NEW YORK — Jay Ruiz’s cellphone rang about 3:30 a.m. on a stifling Saturday.

It was a woman. As usual, she wanted Ruiz to meet her within the hour and take her home.

Ruiz hauled himself off the sofa where he’d been watching TV, jumped onto his bicycle and pedaled swiftly through Brooklyn to the subway station where the caller was due to arrive. Then, after walking her safely to her door, he rode back home, back to his wife of 19 years, and waited for the next call.

This is how Ruiz’s weekends have been since last fall when he saw a video of a shrieking woman fighting off an attacker, which was aired on local TV as police searched for a predator stalking Brooklyn neighborhoods. “That video — I really don’t know why it hit me so hard, but it changed my life,” said Ruiz, who decided to do something.

The next night, he went to a nearby subway station with a friend, held aloft a sign offering to chaperon women home, and waited for customers. The Brooklyn Bike Patrol was born, and 11 months later it has evolved into a borough-wide service with 13 volunteers on call seven days a week, and clients who include doctors, lawyers, tipsy revelers and waitresses working the night shift.

“It’s a real anomaly to have a service like this,” said Elyse Neiman-Seiter, a television producer who first called upon Ruiz in the spring, after she heard about it from someone else, and has used it at least three times. “I think that’s why people at first didn’t believe it.”

Indeed, business was slow at first. “Not a lot of people trusted us,” said Ruiz, who recalled that first night last September, waiting at the station with his friend and hoping for clients. “We stood there for a couple of hours. People thought we were crazy.”

Given the attacks, Ruiz could understand why the women of Brooklyn would be wary of a strange man with a powerful build, a Batman tattoo on his chest and a Kryptonite bike chain around his waist offering to walk them home for free.

But Ruiz, 47, got a lucky break. The Daily News came upon him while reporting on the Brooklyn attacks and did a story on the Bike Patrol. A local news station followed up. Ruiz made fliers, recruited volunteers and set rules: no dating, no taking tips, criminal background checks for every volunteer.

“You have to always have a smile on your face and be over 21,” added Ruiz, who set up a Facebook page with his email and phone number on it and a list of the neighborhoods his volunteers serve, from pricey Park Slope to working-class Crown Heights.

Now, Ruiz and his volunteers, who include a chaplain, a social worker, a college student and a photographer, wear neon-yellow T-shirts that read Brooklyn Bike Patrol, which were donated by a local church, and picture IDs around their necks. A New York senator gave them jackets, and the Brooklyn borough president, Marty Markowitz, has publicly praised the effort.

“You can never have too many extra sets of eyes and ears on the streets,” Markowitz said.

A police spokesman, Paul Browne, said the local precinct had a good relationship with Ruiz and had vetted his volunteers.

Fans have suggested expanding the service to other boroughs. For now, though, Ruiz is sticking to Brooklyn, which like most of New York has seen crime decline but which remains haunted by the 2011 attacks. Browne said police eventually charged three men in connection with the 21 incidents, which spanned from March to October 2011.

New York’s subway runs 24 hours a day, offering cheap transport to the workers and tourists who keep the city humming around the clock. But some of the loveliest neighborhoods during daylight hours can turn frightening in the dead of night, when canopies of leafy trees and shadows of old brownstones turn dimly lit avenues into dark tunnels.

Ruiz was home with his wife, Stacey, when the video of the woman fighting off her attacker, a struggle that lasted more than 30 seconds, appeared on television. The attacker fled.

“I got very angry,” said Ruiz, who by day works as a dispatcher for a bicycle messenger service. “I thought if people had a chaperon from the train stations it would help. Nobody wants to mess with two people. Then it hit me. I could do it on my bike.”

Stacey didn’t object.

“I thought it was a good idea. I just didn’t know if it would work,” she said, joking that if nothing else, it would get Ruiz out of the house so she could have the TV to herself. “I didn’t realize how far it would go — I thought it would just be a little local thing. I’m really proud of how far he’s taken this.”

The system is simple. People call or text Ruiz, whose cellphone shines a picture of his dog, Roxy, when it’s not buzzing, and tell him where and about when they will be leaving a train. Ruiz bikes to the station to wait for the customer or dispatches a volunteer.

One night, he got 17 calls. Some evenings, nobody calls, a sign that reports of street crimes have fallen and people feel safe walking alone.

About the only thing that scares Ruiz, it seems, are rats. “I’d fight Mike Tyson, but I can’t handle a rat,” he said, moving away from a bench after spotting a rat scurrying into a park.

Jumping onto his bike to race across Brooklyn at late hours doesn’t faze the former bicycle messenger, who also spent nearly 20 years coaching Little League and did an Army stint in the mid-1980s. He credits his late father, Ruben, who he says was a wrestler, with instilling in him a sense of chivalry and determination.

Unlike the Guardian Angels or the police, Ruiz and his volunteers do not patrol or carry weapons. Officially, they are on duty from 8 p.m. until midnight on weeknights and until 4 a.m. on weekends, but they try to accommodate people whenever they call. Most customers are women, but at least one man has called for a chaperon.

On Halloween, Ruiz escorted two women — one dressed as a box of cookies, the other as a milk carton — who felt vulnerable because their costumes limited their arm movements. Many of his regulars, who are listed in his phone by their first names and their usual subway stations, are waitresses who work late and who don’t want to spend $20 or so for a cab ride home.

On a recent Sunday, a 21-year-old au pair named Monica Suarez staggered up the steps of a subway station dragging a suitcase and two shoulder bags at 1:15 a.m., about 45 minutes after alerting Ruiz she was en route.

“I was kind of embarrassed to call,” said Suarez, who had just arrived home from visiting Miami and who has been in New York about one year, from her native Colombia. But Suarez knew of Ruiz through a friend and decided to play it safe, rather than make the 10-minute walk through the dark streets on her own.

Ruiz said neither he nor any of his volunteers has been attacked on duty. He credits their bright yellow T-shirts and badges with giving the men an official look that deters troublemakers.

When he started out last September, Ruiz did not envision the service becoming a permanent fixture. But it has taken more than 100 calls since it began, and he expects things to get busy again as summer fades and the days grow short.

“I promised myself I’d do it for a year,” Ruiz said. “I think we have to go beyond that.”

tina.susman@latimes.com