As Israel intensifies its war on Hamas, civilians in Gaza and nearby parts of Israel live under constant threat of aerial assault. Israel's military is launching hundreds of strikes a day on Gaza and said Friday it was moving in ground forces, while Hamas is firing hundreds of rockets back toward Israel. In Gaza, communications and power outages leave civilians struggling to access even basic information about the ongoing conflict. On the Israeli side of the border, an official warning app that gives civilians a chance to take cover is helping prevent casualties.

The Israeli government’s Home Front Command app has warned of 10,000 threats since Hamas first attacked on October 7, the country’s deadliest extremist incursion in years. Adoption has more than tripled since then to over 2 million active users, up from under 600,000, military officials who oversee the technology tell WIRED. Add in unofficial copycats, some of which connect directly to military servers, and “red alert” apps currently account for four of the 10 most popular free offerings on mobile app stores in Israel.

“By providing early warning to civilians, we are saving lives,” says a lieutenant colonel named Itay, who oversees the early warning system for the Israel Defense Forces. Like another IDF officer quoted in this article, he asked that his last name be withheld out of safety concerns. He says his team recently got a message of thanks from a mother saying the app warned of an attack four precious seconds before alarms blared on public sirens that have dotted streets since 2006. “That’s one more child she can get inside shelter,” he says.

The app and sirens are a backstop to Israel’s extensive military defenses. The Iron Dome missile defense system effectively intercepts or destroys most airborne weapons headed to Israel. But some rockets have slipped through, causing injuries in recent days, and the government has encouraged people in Israel to download its app.

Across the border, Israel’s military has sometimes called people in Gaza to warn of its own attacks. But power and communications networks there have been unreliable since Israel’s recent assault began, and on Friday internet access appeared to be cut off entirely. The Home Front Command app doesn’t provide alerts for the disputed Hamas-controlled territory, as it is out of Israel’s jurisdiction, lieutenant colonel Itay says.

Palestinian activists and tech entrepreneurs say no one appears to be trying to provide civilians of Gaza with an equivalent early warning system. Hamas did not respond to requests for comment.

If power and communications were intact, a warning app could technically operate in Gaza, perhaps in a similar way to a system that Western governments fund in Syria. Vetted users and social media scanning tools feed the app with observations about drones, missiles, and other military movement. Machine learning and other data analysis techniques determine which areas of Syria need warning. Alerts then ring through public sirens and messaging apps.

But it’s unclear who would be willing to stand up a system like that in Gaza, or how it could keep functioning as Israel’s assault continues. Communications networks have faltered over the past three weeks of Israeli air strikes, which have damaged key infrastructure. On Friday the last internet provider whose service was operating in Gaza, Paltel, and UK internet monitoring company NetBlocks reported that Gaza was wholly offline. Power generators are reaching their limits, according to the UN agency advocating for Palestinians, after Israel cut off electricity and fresh fuel.

“Tech solutions are invalid,” says Mohammad Alnobani, a Palestinian who is CEO of Arab-focused stock photography service Middle Frame, speaking ahead of Friday’s communications collapse in Gaza. He says trying to maintain contact with anyone inside Gaza right now is frustrating. “We usually lose touch with them and get back in touch every few days to make sure they are alive.”

App Surge

Israel’s smartphone early warning system has its roots in a 2012 side project started by a pair of Israeli software engineers. With sanctioned access to a government data feed, they developed an app now known as Red Alert : Israel to notify people when the street sirens—part of a system known as Red Color—that warn of incoming rockets go off. They aimed to reach people who may not have heard the sirens, perhaps because they were on the edge of town or driving.

Usage first became widespread during violence in 2014, when more than 1,400 Palestinian civilians and six Israeli civilians died, according to the UN. To encourage adoption, the developers designed an option to get alerts sent to the viral social app of the moment, Yo, which was otherwise known only for enabling users to exchange messages saying “Yo.” It later went out of business.

A number of other rocket alert apps emerged, and the user base grew as conflict occasionally flared in Israel and the Palestinian territories over the years. The category got a boost in 2016 when the Israeli government embraced the idea and launched the official Home Front Command warning app.

This digitalization of national security has spread to other countries trying to cope with consistent bombardment, including Syria and Ukraine, where phone-based alerts arm individuals with information to stay safe.

Israelis’ interest in warning apps surged after Hamas militants tore through Israel’s southern border on October 7, killing more than 1,200 people. During the 17 days that followed, the top four red alert apps on Israel's app stores attracted an estimated 200,000 downloads combined, well above the 2,500 downloads in the 17 days before, according to Data.ai, which tracks app markets. Many people who already had the apps sitting dormant on their devices appear to have quickly activated them as the conflict escalated. Over the same period, residents of Gaza have had no equivalent to turn to as they live under the threat of Israeli air strikes and have faced shortages of power, water, and food.

Upgrades and Downsides

Israel’s warning system relies upon a combination of sensors, algorithms, and personnel to identify incoming threats and estimate their target. People in threatened areas receive the loudest possible mobile alerts, with vibrations and light flashes too, even when a phone is silenced. Lieutenant colonel Itay, the IDF overseer, says only milliseconds should elapse between threat detection and the warning, giving most users enough time to scramble for safety.

App users can select additional neighborhoods they want to receive alerts about, a feature that also enables observers around the world to keep tabs on Israel. And Home Front Command can also warn of other emergencies, including earthquakes and tsunamis.

Several critical alerts received this week in California after WIRED downloaded Home Front Command and selected a Tel Aviv neighborhood warned of “rocket and missile fire” and directed recipients to “enter the protected space and stay in it for 10 minutes.” Clicking the alert opened a page inside the app saying users had 90 seconds to reach shelter and listed options such as mamads, reinforced concrete rooms common in Israel; inner stairwells on middle floors of taller buildings; or an outdoor area with hands covering the head.

An IDF major named Shai, in the tech-focused J6 and cyber defense directorate, which develops Home Front Command, says her team of about 10 working on the app have several updates planned. They want to also alert users when threats subside and introduce a kid mode with more digestible notifications for younger users.

Major Shai claims Apple has held up another Home Front Command upgrade that’s been in the works for months, declining to provide details. “This feature would help save lives in this war,” she says. But Israel’s developers need approval from the iPhone maker “for some specific entitlements. I think it’s a technical issue that they want to be sure it’s OK that we can use it,” major Shai says.

Apple spokespeople declined to comment on the state of discussions.

Major Shai says Home Front Command is built to withstand cyberattacks and doesn’t collect personal information, limiting privacy risks. There have been problems with the warning system, though. The IDF says it accidentally issued a nationwide alert on October 11 because of human error. Reviewers of Israel’s official app have complained about it draining their device batteries and lacking customizations offered by unofficial apps, like the ability to change siren sounds to quieter or light-hearted options. (One alert app in Ukraine features the voice of Star Wars actor Mark Hamill.) Lieutenant colonel Itay says Israel’s app has made progress on power usage and doesn’t apologize for its discordant noises. “It needs to get you to do something to stay alive,” he says.

IDF is now working to plug its warnings into the emergency alerting system built into iPhones and Android devices, which power strident push notifications for earthquakes and kidnappings in California and other places. Within days it should launch a warning app for Android TVs, intended to allow alerts to interrupt Netflix and other streaming services as they do conventional TV broadcasts. A Google spokesperson did not respond to a request for comment.

If threats from Hamas grow, IDF could have to consider additional challenges. People have gotten injured by rushing to shelter. In Ukraine, alert fatigue as the war drags on has made people less responsive to calls to shelter. Medical and public policy researchers have suggested better education on responding to warnings. Lieutenant colonel Itay declines to comment.

Some nongovernment apps, such as news app Walla, receive rocket alerts directly from government servers. Others seem to scrape data, leading to notification delays of a couple of seconds. Lieutenant colonel Itay contends that none of the unofficial options match the IDF app’s precision and speed—and it’s not cluttered with ads. “Home Front Command is the only one you can rely on,” he says.

He may be onto something. Since the October 7 attack, the independent app RedAlert – Rocket Alerts, which has unique features including a countdown timer for sheltering, has blocked access to anyone outside of Israel, claiming there was “a coordinated, worldwide DDoS attack” on the service, the app’s developer Elad Nava wrote in response to app store reviews, referring to a bombardment of traffic designed to overwhelm servers. Location-based alerts also are turned off due to Android limitations that limited their reliability, Nava wrote in another review response. Internet security company Cloudflare on October 13 found a website, since removed, hosting a malicious Android app impersonating Nava’s own. Nava did not respond to requests for comment.

Days after the Hamas attack, hacktivist group AnonGhost claims to have breached Red Alert : Israel, according to cybersecurity company Group-IB. Erroneous alerts went out to up to 20,000 users, the hackers claimed. The app is no longer listed on Google Play but remains on Apple’s App Store. The app’s developer, Kobi Snir, did not respond to requests for comment. Overall, AnonGhost discussed attacks on four separate red alert applications, though significant disruptions appear to have been limited, and the group moved on to other targets, according to Group-IB.

Lieutenant colonel Itay says the government won’t choke off unofficial apps. “It’s a democratic state,” he says. “We are giving you a seatbelt. If you don’t want to use it, that’s your choice.” A life-preserving option for at least some civilians put at risk by the war. While Gaza is offline, bullhorns or air-dropped leaflets may be the only warnings its residents will have as Israel’s assault escalates.

Updated 10-28-2023, 1:45 pm EDT: This article was updated to remove the last names of IDF officers, after a post-publication request raising safety concerns.