As fire was billowing through residential neighborhoods in Lahaina on Aug. 8, emergency managers for Maui County sent out an evacuation alert that would blare on the cellphones of anyone near the blaze.

“Evacuate your family and pets now, do not delay,” the warning said.

But many people most in need of the alert said the message never reached their phones, leaving them scrambling for safety as the fire began roaring toward their homes. More than 100 people died in the inferno, and some survivors wondered why they had not been notified earlier that the situation was out of control.

“I probably could have saved my animals,” Barrie Matthews, 70, said as she tearfully recalled her family’s desperate effort to escape. “We just had to go. We had to leave five of my cats. I can barely live with myself.”

As more households disconnect landline telephones and fewer families have access to broadcast television and radio, emergency managers have increasingly focused on wireless emergency notifications to instantly reach large numbers of people. But that modern system has its own limitations, relying on the resilience of cell networks and the proficiency of emergency crews across a patchwork of local agencies.

Launched in 2012, the Wireless Emergency Alerts system was designed to allow federal, state and local authorities to send messages about severe weather, unfolding disasters and abducted children on a single, uniform system. It has been used tens of thousands of times and will be part of a nationwide test of emergency warning systems set to take place Oct. 4.

Unlike television, radio, road signs or social media, emergency managers can use wireless alerts to target specific neighborhoods with an alarm that can wake someone from sleep or jar them to attention.

Jeannette Sutton, a professor at the University at Albany who specializes in disaster warning alerts, said the system can be messy. There is little guidance for agencies on how to formulate the alerts, so they can sometimes go out with missing information or confusing instructions. They are often left to be sent by emergency personnel who are busy trying to fight fires or control floods.

When the system is operated correctly, Sutton said, it acts like a siren in thousands of pockets, giving the authorities the ability to warn the right people at the right time. An upgrade several years ago expanded how much text can be included in each alert, allowing for more detailed guidance on how people can keep themselves safe.

“It is vital,” she said. “It is absolutely necessary. It does save lives.”

On Maui the first signs of the afternoon fire came around 3 p.m., when video showed smoke blowing down a hillside.

As the blaze began moving into the neighborhood below, some residents began evacuating on their own. Others said they struggled to see what was happening or where to go, with some saying they assumed the smoke in the distance was a fire that would soon be under control. Soon, however, the fire gained momentum and was igniting houses in its path.

Records show that it was only at 4:16 p.m., after the fire had begun moving through town, that the county sent an emergency cellphone alert. It was sent to a portion of the town’s residential area east of the commercial district. But it did not cover the Front Street area along the waterfront or the other neighborhoods to the north and south, which were soon overrun with fire.

Matthews said that at her home on the south side of town, she saw the smoke to the north of her and began checking media sources for updates. She got in her car and flipped through all the AM stations, then the FM ones, but they were all on regular programming. She went back in the house and flipped through television stations but saw no sign of trouble. No alerts popped up on her cellphone.

The county has said it did not activate its audible warning sirens, fearing that people would think a tsunami was coming.

“I thought somebody would let us know what was going on,” Matthews said. “There was nothing.”

Suddenly, she said, the fire was just a couple of blocks away. She said she and her husband scrambled to collect their many animals and her ailing father. But they did not have time to gather all of their cats.

Many residents said they never got an alert. Others said they did.

Emergency management officials did not respond to requests for comment about how the Maui wireless alerts were handled.

A range of technological factors can determine whether an alert gets through, including whether a cellphone is in the zone targeted, whether it is turned on and whether it has cell coverage. The age of a phone can also influence how it receives an alert, as newer devices are calibrated to receive alerts targeted to more specific geographic areas.

On Maui one resident with an older phone received the Lahaina alert even though she lived on the other side of the island and never came near the fire. Some residents with newer phones were near the evacuation zone but did not receive any alert, perhaps because they were just outside the targeted area. One such family said they had several newer-­model cellphones with them as they were driving down Front Street before the fire reached there, but none of them received emergency notifications; a much older phone used by one of their children did get an alert.

Some who received the alert said it may have saved their lives. Breanna and Glenn Gill were taking a nap at the Lahaina Shores Beach Resort when the emergency alert came at 4:17 p.m., blaring on their phones, waking them up.

Glenn Gill opened the shade of their hotel room and saw the hillside ablaze above them. They were able to evacuate.

Residents reported that cellphone coverage was spotty that day as the town dealt with power outages and high winds. Cellphone service in the area of Maui where the fire occurred is largely dependent on overhead fiber lines, and as the fire spread, those lines were damaged.

An AT&T spokesperson, Jim Greer, said the fiber infrastructure that serves all wireless carriers in the area was burned. While lines are buried in many parts of the country, Greer said the volcanic rock on Maui makes that a challenge.

Sutton said it was important to build more redundancies into the emergency alert system, look at burying cables to make it more resilient and remember that the wireless system cannot be relied on alone to warn people that danger is imminent.

“It’s one layer in the many potential strategies,” she said.