You Can Still Use a Pager in 2023

How a Raspberry Pi will help you resurrect this classic communications device

Pagers were popular many years ago, and some people may still have one at home. Is it possible to test the pager now? Absolutely, and I will show you how to do it.

Let’s get started.

POCSAG — The Messaging Protocol

In the 90s, I was a student and the pager for me was something like a Star Trek Communicator, a piece of cutting-edge technology. It is fun to remember it because now I know that technologically the paging protocol is very straightforward. From the encoding perspective, the pager is not so different from the wireless doorbells that are selling now for 5$ in Aliexpress.

Let’s say we want to send a message “TEST” to the number “1234”. The message in a binary form will be looking something like this:

10101010101010101010101010101010 - Preamble
01111100110100100001010111011000 - Frame Synchronization Code
01111010100010011100000110010111 - Idle codeword
00000000000100110101111000111111 - Address + Function Bits + CRC
10010101101000111001001111111100 - T E S (7 bit/symbol)
11001010100000000000001111100011 - T . .
01111010100010011100000110010111 - Idle codeword

And this is how the message looks on the radio spectrum:

Bits are encoded with a frequency shift keying (FSK) modulation using 9 kHz bandwidth and 1200 bits per second speed. All this message is transmitted in about 0.5s.

It looks simple, and it really is. I will skip the details; those who are interested can read the protocol specification. It is even easy to draw all these bits with pen and paper — these protocols were simple in the past. I think nobody can do it with modern GSM or WiFi. In POCSAG messages, there is no authentication, no security keys — all messages to all paging company customers are available on-air “as is,” and by the way, can be easily decoded with PC software like PDW. Some modern pagers, like Swissphone X15, have optional encryption support, but they are…