Woken up by midnight phone alert? Inside Kerala's heavy rain warning system

In the early hours of last Sunday, thousands of people across Kerala were jolted awake by a loud emergency alarm blaring from their mobile phones. Many, startled by the unfamiliar sound, reached for their devices expecting a call, only to find an urgent warning about extremely heavy rainfall in their area.

The alert was sent to almost every active mobile phone in districts under a red alert, leaving many wondering how the message reached their phones, even when they were on silent mode.

Disaster management authorities have urged people not to ignore these high-decibel warnings during the monsoon. According to Sekhar Kuriakose, Member Secretary of the Kerala State Disaster Management Authority (KSDMA), the system is designed to wake people in high-risk areas, even if they are asleep, and ensure timely warnings reach everyone before disaster strikes.

The alert was issued through SACHET, India's National Disaster Alert Portal, a nationwide emergency communication system jointly operated by the National Disaster Management Authority (NDMA) and the Department of Telecommunications (DoT).

Developed by the Centre for Development of Telematics (C-DOT) under the DoT, the platform enables authorities to broadcast emergency alerts simultaneously to millions of mobile phones during natural disasters and other life-threatening situations.

The system complies with the Common Alerting Protocol (CAP), an international standard prescribed by the International Telecommunication Union (ITU), and is now operational across India.

Why it rings even on silent mode
Unlike a regular SMS, the SACHET system uses cell broadcast technology, which sends alerts directly through nearby mobile towers rather than as individual text messages.

Because of this, the warning can override a phone's silent or Do Not Disturb (DND) settings, triggering a loud alarm and displaying the message prominently on the screen. Even if a user is on a phone call or using an app such as WhatsApp, the alert temporarily takes over the display.

The alerts are geo-targeted, meaning only users physically present in the affected area receive the warning. They can also be delivered in multiple regional languages to ensure maximum reach.

How the alerts are sent
The process begins when an agency such as the India Meteorological Department (IMD) issues an official warning about an impending hazard, such as extreme rainfall.

After the warning is validated by disaster management authorities, it is forwarded to C-DOT's central CAP aggregator. The information is then transmitted to telecom operators, who instantly broadcast it to all compatible mobile phones within the designated geographical area.

According to KSDMA, this intrusive alert mechanism is used only for critical, life-threatening emergencies where immediate public action is essential.

Beyond mobile phones
Until recently, disaster warnings relied largely on physical sirens. However, Kerala has only 126 disaster warning sirens, making them inadequate during widespread emergencies. Social media, meanwhile, cannot be relied upon for urgent overnight alerts.

The SACHET platform addresses this gap by delivering warnings directly to people's phones within seconds.

Authorities are also planning to expand the system further. In the next phase, emergency alerts will be integrated with television broadcasts, allowing live programmes to be interrupted with on-screen warnings during disasters.

The platform can also be used for hyper-local emergencies, such as a chemical tanker leak or industrial accident, enabling alerts to be sent only to people within a specific danger zone, helping prevent them from entering hazardous areas.