Jamie Adams


Analysing Pager Traffic with a Cheap USB Radio

I’ve been having some fun with a cheap USB FM/Dab radio. With some clever software this little gadget can do a lot more than it was designed to do, including decoding pager messages. People really do still use pagers.. The pager as we know it was invented in 1956 by Multitone Electronics for use in London hospitals, but it was Motorola who gave the device a name and introduced it to the masses. The popularity of the pager surged in the 1980s as it became the must have gadget of professionals. Teenagers and pop stars jumped on board in the nineties and it looked like the pager was here to stay - but as pager use grew so did the mobile phone network which eventually supplanted it. Mobile phones became more reliable, affordable and feature rich and usage of pagers dived.

Pagers still have some advantages over mobile phones. Coverage tends to be better, especially indoors and their battery life can be measured in weeks rather than hours. They can be used in places where mobile phones are banned for security reasons, or where they might interfere with sensitive equipment. Pager messages are broadcast in clear text by powerful transmitters over FM radio bands. You’ll need a cheap USB DAB/FM radio receiver to decode them. I bought mine for less than a tenner.

A search for ‘sdrsharp pager messages’ should give you give you all of the info needed to get up and running. For the technically inclined, the system works by modulating a tone between two frequencies to create a binary stream. The transmitter alternates these frequencies very quickly – up to 6400 times a second. Here’s a sample of some of the messages that I decoded:

0101158 23:39:12 29-07-15 FLEX-A  ALPHA  3200  FROM GLOUCESTER POLICE CONTROL ROOM, 
HAVE ASKED EVERYONE AND NO POLICE OFFICER HAS THE KEYS THAT HAS BEEN MISLAID. TEL NO 
IS 101 IF YOU NEED TO CALL.

0121305 23:01:17 29-07-15 FLEX-A  ALPHA  3200  PLS CALL ANNE AT OBSTETRIC THEATRE 
ON 458 47`` 

0118459 23:58:43 29-07-15 FLEX-A  ALPHA  3200  20150729 23:57 boc1web03.servstream.
com:conn CRITICAL ALERT 

0119043 23:58:45 29-07-15 FLEX-A  ALPHA  3200  Room S17 Isolator Z21 Hatch Pressure 
BMT  42.5 (Alm:D Lmt:<50.0000 Grp:BMT)

I’m surprised that no effort is made to encrypt the messages because many of the messages contained personal details such as names, addresses and phone numbers.

Warning:Whilst it is extremely unlikely to get you in trouble, decoding pager messages is illegal. See Section 48 of the UK Wireless Telegraphy Act: http://www.legislation.gov.uk/ukpga/2006/36/section/48

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