Ask HN: How Do Emergency Alerts on Phone Work?

by rishikeshson 3/3/2026, 6:27 AMwith 4 comments

I’m now in UAE which is affected by war. Woke up to an alert yesterday night and was wondering how this works. Any good write ups on its technical side?

by WarOnPrivacyon 3/3/2026, 6:37 AM

     Delivery Method: WEA utilizes a one-to-many alert delivery service
     called SMS-Cell Broadcast (SMS-CB), rather than SMS Point-to-Point
     (SMS-PP). 

     SMS-Cell Broadcast (SMS-CB) is a method for sending short text messages
     simultaneously to multiple mobile phone users within a specific geographic
     area. It is a feature within the GSM (Global System for Mobile
     Communications) standard and is sometimes referred to as Cell Broadcast.
ref: https://www.etsi.org/deliver/etsi_ts/144000_144099/144012/07...

by david_allisonon 3/3/2026, 4:29 PM

Might as well start with the source code[0] and dig deeper:

* CMAS https://en.wikipedia.org/wiki/Wireless_Emergency_Alerts

* ETWS Earthquake and Tsunami Warning System

[0] https://cs.android.com/android/platform/superproject/main/+/...