HOUSTON — The immigration raid early Monday morning at the El Paraiso Apartments in Houston was not exactly a major victory for law enforcement. It was foiled, in part, by 19-year-old Kaylin Garcia.

Shortly before 7 a.m. Monday, Ms. Garcia was sitting in her car near her family’s apartment, in a largely Hispanic section of southwest Houston about 15 miles from downtown. She saw four Immigration and Customs Enforcement agents walk by — one dressed in camouflage fatigues and the others wearing black T-shirts and bulletproof vests. They were knocking on apartment doors. She took a picture of the agents with her phone, posted it to her Facebook page and notified some of her neighbors.

At least one of her neighbors saw Ms. Garcia’s picture and heard about her warnings — the family slid the chain closed on their door. When the agents knocked on the door, the family — an undocumented Honduran man and his wife, along with their American-born children and another relative — kept silent and never opened it. After a minute or two, the agents left.

“I wasn’t scared,” Ms. Garcia said. “I was scared for my neighbors.” She added, “Nobody opened the door.”