Wow. Two posts in less then a week! I’m on a roll! Don’t get used to it though. I’ve only waited ountil the first day of the decade so nobody could say I didn’t post anything this decade. .

When someone talks about pagers, most people imagine old devices that were used before cell phones were a thing. They can be used to transmit numbers or short messages, mostly to tell someone to call a specific phone number.

You would think that, in the age of huge smartphones and super fast and reliable mobile internet connections, there would be no more use for these small dumb devices. Well, you’re wrong! Although two pager networks were shut down in 2005, one is still alive (KPN Nationaal 3). It used the POCSAG encoding and transmits messages at 1200 baud per second. It broadcasts on 172.450MHz).

Tuning my Baofeng (which is a popular cheap Chinese radio) to that frequency, you can regularly hear some beautiful noises

Ah, don’t you just love the sound of POCSAG?

These messages are unencrypted and transmitted over the air. So that means that anyone can tune to this frequency and read pager messages. Isn’t that just great?

So I setup my Raspberry Pi, plugged in an antenna and fired up rtl_fm and multimon-ng.

ugly setup pager messages

Here are some interesting examples of messages I received:

  • [REDACTED ADDRESS] - Hal 4 (M33*HAL4) 29-12-2019 16:30.32 RK4.2.1-3 - Hete Cellen RK4-2-1-3(3) Life Check 2 BlueID, Life Check BlueID B Uit Geen
  • Koppert - Data manager (KBS*B01) 29-12-2019 16:30.02 RK1 - Technische ruimte RK1 - Datamanager(1) Life check 2, Life check Geen
  • [Van:]CheckMK@ggdflevoland [Onderwerp:]Check_MK: W2K8-SQL-10 - DOWN - UP [Inhoud:]Host: W2K8-SQL-10 Alias: W2K8
  • (0143) ENERGIE WK 2 Externe storing in WK
  • :[AC-Notify] Zorg_18_Portaal/ is UP - NID[372484]
  • 52/2/CH/mz-01/522CHmz-01_P0/P0Metaalzoutendosering niet in bedrijf
  • 2342 Radix (WURplant) 29-12-2019 16:00.03 Schoutenhoef Netwerkmanager(1) Test melding, Testmelding (OS1) B Uit Geen

So, messages from monitoring systems, industrial alarms and other things I don’t understand or I’m missing the context to. Oh by the way, If you need help with that SQL server hit me up.

Most of the messages I see are junk, though. I don’t know if that has something to do with my receiver or if these are secret messages for spies deployed in the Netherlands.

I also realised I don’t really know a lot about pagers. There are these codes next to each message called ‘CAP’ code (Channel Access Protocol code). These are, in some way, compareable to phone numbers. But multiple pagers can have the same CAP code and one pager can (if the model allows it) store multiple CAP codes. Useful for when you want to send one message to a group of people, just program all the pagers with the same CAP code.

I can imagine most people either didn’t know pagers were still being used (and how much they are still being used!) or that the messages are unencrypted and can be read by anyone with a €20 RTL-SDR dongle or some other cheap radio.