POCSAG: the paging that won't die

We thought they vanished with the 90s, but pagers are still here — for a good reason. Where a mobile network saturates or fails, a POCSAG message broadcast by a powerful transmitter gets through everywhere, instantly, to thousands of receivers at once. Hospitals, firefighters, emergency services and industry still rely on it.

What you can pick up, and what you can't

In Europe, paging often lives around 466 MHz — right within an RTL-SDR's reach. It's POCSAG, a 1982 protocol:

FSK modulation: the information hops between two close frequencies (typically ±4.5 kHz). On the Le waterfall (cascade temporelle), a narrow burst (~16 kHz) appears, lasts a fraction of a second, then goes quiet.
Rates 512, 1200 or 2400 baud. Simple structure: a preamble, "batches" of 32-bit words with error correction (BCH).

OpenHertz deliberately stops at presence detection: spotting the burst, not reading the message. Decoding POCSAG in the clear potentially exposes personal data — medical calls, contact details, operational alerts. Receiving a wave is one thing; exploiting its content is another, legally very different (Légal & sécurité).

Detecting ≠ decoding (again, always)

Same honesty principle as for drones: seeing that "something is happening" at 466 MHz is easy and harmless. Going further engages your responsibility. The mission lets you watch paging live on the spectrum — the exciting, legal part.

Recognising a paging burst

Regularity: bursts often come grouped, at intervals, when a broadcast cycle goes out.
Width: ~12–20 kHz, far narrower than a WiFi channel, wider than a pure carrier.
Sound (if you demodulate it as narrow FM): a characteristic "modem" rasp, like an old fax.

👉 Catch paging in action: POCSAG pagers