Tech Explained: Cell Broadcast

Posted under Tech Explained, Technology on May 3rd, 2026 by

Yesterday many of you in India may have received the test alert with your phone going off in vibration and sound mode from the Govt. It got me to look up the tech stack that enables this. I wanted to explain it because it looks like an SMS, but it really isn’t.

Fundamental tech is called Cell Broadcast. It’s a one-to-many setup. A tower broadcasts an alert to compatible phones connected to that cell. Your phone does not need mobile data. It only needs to be in coverage area. Whereas SMS is one-to-one. The network sends a message to each phone number. That is fine for normal updates, but millions of messages can slow down during a cyclone, earthquake, gas leak or war.

Indian stack seems built around SACHET, the National Disaster Management Authority’s CAP-based (Common Alerting Protocol) Alert System, developed by C-DOT. Visualise it as an alert form that carries the event, area, severity, language, action and expiry time.

I think the flow might be something like a Govt agency like IMD creating a warning. SACHET validates and routes it. C-DOT’s Cell Broadcast system connects it to telecom operators. The operator maps the area to towers, and then selected towers broadcast the alert directly to phones. 

Once the tower broadcasts it, the phone’s modem listens for that alert channel and passes it to the OS as an emergency alert, not as a normal inbox message. That is why it can pop up with a loud tone and vibration without needing mobile data. In SMS, the network addresses your number and waits to deliver a message to you individually.

It can work on basic phones too, but only if that phone supports Cell Broadcast. If the phone is off, in airplane mode or out of coverage, it will not receive it.

I read that SACHET is not only for mobiles. The same platform can push warnings through SMS, Cell Broadcast, apps, TV, radio, social media, railway station boards, and coastal sirens. Its scale is impressive from a tech POV.

BTW: A Cell Broadcast alert does not need your phone number to reach you, just being in coverage is fine.

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Advanced Tech: Ghost Murmur

Posted under Advanced Tech on April 26th, 2026 by

You might have seen news a few weeks back about the rescue of a US pilot from Iran. Then came a media post from NewYorkPost about Ghost Murmur, a device that supposedly helped find him by detecting his heartbeat 60km away. There was a lot being said about it. I wanted to see if this was scientifically possible. It’s defense tech, so this will be slightly speculative from my end.

The claim made is that your heart creates a tiny magnetic field when current flows through it. A sensor picks it up and an “AI” software filters the noise and looks for a heartbeat pattern.

I deep-dived into it. There was a base technology that kind of enables it. It’s called Quantum Magnetometry. This was shown with NV centers in diamond. NV means nitrogen-vacancy. In simple terms, one carbon atom in diamond is replaced by nitrogen, and the neighbouring carbon atom is empty. When you shine laser light and apply microwaves, its quantum state changes slightly with the magnetic field around it. By reading that change in light, the diamond can act like a very sensitive magnetic-field probe.

So the probing tech is real. Many research groups work on NV-diamond magnetometry, and heart magnetic signals are also real. But heartbeat magnetic field is a very weak near-field signal. Near the chest, it may be in the picoTesla range, which is already tiny. A picoTesla is one trillionth of a Tesla. For reference, Earth’s magnetic field is usually around 25-65 microtesla.

And once you move away, that signal drops very fast. So I highly doubt they have somehow magically solved the problem that it survived kilometres of air, terrain and Earth’s magnetic field. They claim AI software, but AI can kick in only if the data capture is possible. So detecting one human heartbeat from 60 km away feels extremely unlikely based on public physics. I do think the claim is an overexaggeration from someone either to mislead or oversell.

Realistically it might be a sensor fusion. Maybe like a rescue beacon, GPS burst, thermal imaging and maybe some magnetic sensing all feeding one system.

What do you folks think?

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