The alert flashed across the screen of Christina De Leon’s iPhone on a recent morning: “Someone needs your help.”

De Leon, 36, answered the video call and saw a middle-aged blind man on the other end who said he needed help finding one of his dining room chairs.

It was the fourth call from a visually impaired person that De Leon got through the smartphone app Be My Eyes, but it was the first one she had been able to answer. She was nervous.

“I didn’t want to mess up or anything,” said De Leon, a photographer who lives in Fresno, Calif. “But I loved it.”

She was able to guide him to his chair. He thanked her, and they both hung up.

The free app connects visually impaired people with sighted volunteers for help with daily tasks, such as matching an outfit or picking out the right spice. A blind user connects with one of 1.8 million strangers, who speak more than 180 languages, for help figuring out the color of a shirt or the location of missing keys.

De Leon isn’t the only one who loved it. Last month, pop singer Bea Miller called it the “purest thing ever” to her more than 800,000 Twitter followers.

And her followers, some of them also volunteers, responded:

Plenty of other people have taken to social media to say that answering a quick call to help a blind person is “so awesome.”

It’s the most popular time of year for giving, but some people shy away from pledging their time to help others because they feel overwhelmed in a flurry of holiday gift-buying and travel. Yet interacting with people while volunteering is the most emotionally rewarding way to give, according to Ashley Whillans, a professor at Harvard Business School who studies how people navigate trade-offs between time and money.

“If you give time away, you actually feel like you have more of it,” Whillans said, explaining that we often are not as busy as we think we are.

The Be My Eyes app has attracted more than 100,000 visually impaired users since a Denmark-based team launched the app in early 2015. When one of those users makes a call for help on his iPhone or Android device, 10 randomly selected volunteers get alerts on their own phones.

The first person to answer sees a video image of the blind user’s environment and tries to help resolve their issue. A volunteer may read the label on a soup can, look around a caller’s house for a missing object or do one of hundreds of other tasks that can be difficult for people with impaired vision.

“Sometimes it’s a quick fix, other times it’s a longer conversation of what’s life like where you are,” said Christian Erfurt, the chief executive of Be My Eyes. “That reminds us that we’re not that different, and the gap between ‘us and them’ is minimized.”

People who are visually impaired can use accessibility features to make calls from smartphones. The software uses speech and touch to communicate with users. Some phones also offer increased text sizes or color contrast to help people with low vision.

In the two years that she has used Be My Eyes, Alaina Walker has made more than 10 calls for help. Although she said she most often uses the app for guidance matching her outfits, she has also called volunteers for help determining if her oven was on and navigating from a bus stop to a nearby dollar store.

Walker, who is visually impaired, said she gets excited when she connects with a volunteer from her state of Alabama or from a different country.

“What I think is cool about it is it’s anonymous,” said Walker, a 43-year-old makeup saleswoman. “Some people are so self-conscious about asking for help.”

Be My Eyes doesn’t do background checks on its users or volunteers, although rules of conduct and respect are published on the app’s website. The company gives everyone “the benefit of the doubt,” Erfurt said, and bans people if someone reports their behavior as abusive more than once. Erfurt said the company relies on the assumption that the app’s users will see any inappropriate behavior as simply bad apples.

That proved true for Pittsburgh-based volunteer Jacqui Giordano. When a caller once asked for her phone number, she said, she declined and assumed the uncomfortable experience was an anomaly.

Giordano’s second call through Be My Eyes was far more successful. Several family-related issues had left her crying before work one morning in August when a visually impaired user called to ask for help matching a pair of colored jeans to a shirt and scarf. The call was no more than 15 minutes, but Giordano said she probably would never forget it.

“It came at the right moment, because there were struggles going on in my life, and I thought, ‘There is still good in this world,’” said Giordano, 37.

For many volunteers, calls for help come infrequently. Giordano said she has received only about five calls since she signed up in the summer. That feature is intentional, according to Erfurt, who said visually impaired users connect with strangers so the users don’t feel as if they’re bothering anyone.

Diane Giannetti, 67, who has been blind since birth, said she appreciates making the random connections and she likes that she doesn’t have to pay to use the app. Person-to-person calls are always free on Be My Eyes. Visually impaired people can also use the app to call Microsoft for free customer service with Microsoft products, and Microsoft pays Be My Eyes to facilitate those calls, which keeps the app running for free.

Giannetti, who lives in Connecticut, said she primarily uses the app when her sighted relatives aren’t home to help her with various tasks. It gives her a measure of comfort that she has people at her fingertips who are willing to help if she is without her sighted family members for several days.

“I wouldn’t be nervous,” Giannetti said. “Because I know they’re only a phone call away.”