... because PDF Warning: 1/2 of active shooter scenarios are over in 5 minutes. Like earthquakes, we don't get warning minutes before the event because of seismometers and +$100,000,000 in detection and automated warning systems. With easily verifiable information and buildings built to resist them.

If you're at a university, they're required to have mass alert systems. They also know their community and can push it to the people who were smart enough to give their college their actual phone number rather than some random shit or not bother to update it when they changed their number.

Everyone else though? Good luck dropping a geofenced 911 alert with actually relevant information besides what people should already know. Run, Hide, Fight. It's literally all that's sent out in any of those college emergency alerts. MAYBE a hall location/area if they got non-panicked lucky info with someone calling Security instead of 911.

After action reports, and debriefs are easily available for most of these events if you want to read them. The FBI and DHS have a LOT of info too.

https://www.fbi.gov/file-repository/active-shooter-incidents-in-the-us-2022-042623.pdf/view