Since Donald Trump’s war on Iran started more than three weeks ago, United States military forces have allegedly attacked more than 9,000 sites, creating a climate of fear and constant uncertainty for Iranians in Tehran and across the country. Without an advanced warning system from the government, and amid the longest internet shutdown in Iran’s history, Iranians are left in an information void.

Even before Israel and the United States began dropping bombs, Iran’s lack of a public emergency alert tool and severe state-controlled digital oppression has impacted tens of millions of citizens. Since the 12-day Israel-Iran war last year, though, a group of Iranian digital rights activists and volunteers has been working to fill the gap with a dynamic, regularly updated mapping platform called Mahsa Alert. The project can’t replace real-time early alerts that could come from a coordinated government service, but the tool sends push notifications when Israeli forces warn about attacks, details some confirmed strike locations, and offers offline mapping capabilities.

“There is no emergency alert in Iran,” says Ahmad Ahmadian, the president and CEO of US-based digital rights group Holistic Resilience, which is behind Mahsa Alert and has been developing the platform since last summer. “This was where we saw the traction, we saw the need, and we continued working on it with the volunteers, with some [open source intelligence] experts, and used this to map the repression machinery ecosystem of Iran and surveillance.”

Mahsa Alert is a website but also has Android and iOS apps, which were intentionally designed to be lightweight and easy to use on any device. Given the heavy government connectivity control inside Iran and erratic access to the internet, volunteers also prioritized engineering the platform for offline use. And it can be easily updated if a user does get connectivity for a brief period by downloading APK files that contain new data. The team works to keep these updates extremely small; a recent release was 60 kilobytes, and Ahmadian says they are typically no more than 100 kilobytes.

One overlay on Mahsa Alerts plots the locations of “confirmed attacks” that Ahmadian says his team or other OSINT investigators have verified, using video footage or images that are submitted to a Telegram bot or shared on social media. There are also warnings about areas where Israeli forces have issued evacuation alerts, along with the crucial component of people submitting reports on what is happening around them.

“We have to go through a due diligence and verification process and tag them before putting them on the map,” Ahmadian says of the reported attacks and incidents, adding that the team has a backlog of more than 3,000 reports that it is working through or is unable to verify. Along with attempting to map strikes, the team behind Mahsa Alert have also plotted “danger zones” that could be at risk of attack—such as sites linked to Iran’s nuclear program or military—so ordinary citizens can stay away from them. Ahmadian claims 90 percent of attacks it has confirmed were at sites that were already present on the map. “Some of them that we can confirm, we do it because [a user] has shared a photo or they have shared some details that makes them verifiable,” he says.

The map also includes locations of thousands of CCTV cameras, suspected government checkpoints, and other domestic infrastructure. Medical facilities, such as hospitals and pharmacies, are included on the map along with other resources like the locations of religious sites and past protests.

Mahsa Alert has become more visible on global social media feeds as Iranians around the world share details from the map, encouraging people to look into the service and flagging it for friends and family who could use it as a resource. “The app went from near zero to over 100,000 daily active users in a matter of days,” Ahmadian says, adding that in total there have been around 335,000 users this year, with people first turning to the app during the Iranian regime’s brutal crackdown on anti-government protesters in January. Through the limited user information the app collects, Ahmadian claims there are signs that 28 percent of users are accessing the platform from inside Iran.