“I’m 84 years old, so staying confined to the house for protection,” wrote Marcia Savin, a children’s book author and teacher who lives alone in the Cobble Hill section of Brooklyn, on the neighborhood social networking app Nextdoor.

It was Saturday, March 21. Her prescriptions were ready at a local pharmacy, she said, but she couldn’t pick them up “because I’m not leaving the house and they have stopped answering phone.”

Soon, she said, she received five offers to help. “None of them were people I know,” Ms. Savin said in a phone interview on Tuesday. “It’s been quite heartening. This has been the only good side to all of this — the community reaching out.”

So far, Laura Weiland, 32, has made two drop-offs at Ms. Savin’s home. Their interactions are simultaneously neighborly and distant. “I’m completely confined,” Ms. Savin said. She doesn’t open the front door. “I see the person, I flip the check through the mail slot, I tell her to leave the supplies and I drag them in,” she said.