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FORTUNE — Manpower — SWAT teams, bomb squads, K9 units, scores of local police officers, and citizens providing information — will forever receive credit for bringing down the suspects linked to the Boston Marathon bombings that killed three and wounded hundreds. But there was another, little-noticed participant in the manhunt: an emergency alert platform created by Glendale, Calif.-based Everbridge.

It was Everbridge’s system that enabled officers to keep locals informed — and safe — as they tore through suburban streets in search of the suspects. Everbridge allows single entities to send thousands of messages at the push of a button, even if cell towers are down. (The system can send texts using Wi-Fi). During Boston’s marathon bombings, local companies used the system to verify the safety of employees, hospitals used it to relay information to nurses, and police updated citizens with safety alerts and messages. “We really wanted to limit people being out [on the streets] so that those law enforcement folks could maneuver around the town,” says Watertown Fire Chief Mario Orangio. “By getting that message out as quickly as we did, it helped immensely.” At one point during the manhunt that resulted in the capture of suspect Dzhokhar Tsarnaev, the Watertown Fire Department sent out 11,000 messages in a 15-minute span using Everbridge, he added.

Everbridge, which was founded in 2002 following the September 11 attacks, has essentially replaced the phone tree, an inefficient and often ineffective way to spread emergency alerts in the 21st century. Everbridge’s system not only sends out messages but also gathers information by prompting receivers to use short, simple responses. Questions like “Are you safe?” or “Do you need medical help?” are examples of messages that would allow receivers a chance to send important information back to authorities, says Everbridge CEO Jaime Ellertson. At Children’s Hospital in Boston, Everbridge is used regularly to help staff nurses, says Nicholas Levitre, the hospital’s emergency management coordinator. During the chaos following the bombings, Children’s used the system to get nurses onto important conference calls, a task that used to require sending out individual pages using the telephone. “Information was changing so rapidly,” says Levitre, “that we just needed a way to get it out quickly.”

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In other instances, the Everbridge system can be programmed to repeatedly call people until they answer the phone, a task more or less impossible with the old phone tree system. “Communication by itself probably isn’t the difference between life or death,” says Ellertson, “but it certainly can be the difference between keeping people safe or not.” Everbridge customers currently reach some 35 million Americans, from urban jungles to the plains of tornado alley.

The role of Everbridge’s technology is, somewhat unfortunately, more important than ever. Both natural (Hurricane Sandy) and unnatural (Newtown shooting, Aurora theater shooting) disasters in the last year have turned a bright spotlight on the need for emergency alert systems. Virginia Tech University is an Everbridge customer, adopting the system after a 2007 school shooting left 33 dead, including the killer. Everbridge also claims the City of New Orleans (Hurricane Katrina), the state of Connecticut (Sandy Hook Elementary shooting), and Los Angeles’s LAX airport as customers. During Hurricane Sandy’s rampage on the northeast in October, Everbridge customers sent out a total of 12 million messages in a 3-day period.

As a resident of Sudbury, Mass., just 23 miles outside of Boston, CEO Ellertson saw his company’s system in action from a citizen’s standpoint. (His 15-year-old son was just two blocks from the marathon’s finish line when the blasts went off.) Everbridge’s Boston office was shut down, but its office in Los Angeles handled all of the system’s traffic. “We had a flawless performance,” says Ellertson. At the end of the week, after Tsarnaev was captured by police in Watertown, the City of Boston had one final Everbridge message to send to its residents: “Thank you.”

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