Turn off the mobile

Ian Batten igb at batten.eu.org
Thu Jul 17 13:24:21 BST 2014

On 17 Jul 2014, at 11:55, Wendy M. Grossman <wendyg at pelicancrossing.net> wrote:

>  The pager still has to be locatable in order for you to get the
> page, right? 

No, old-style pagers are receive only.  Each page is transmitted on all transmitters, 
once (or at most a few times), and if your pager receives it, good, if it doesn't,
tough.  That's why pagers can run for a month or more on a AA battery: they're just
a simple receiver. If memory serves, the paging frequencies are adjacent to the
the 144MHz/2m and 432MHz/70cm amateur allocations.  You're hardly going to manage 
two-way communication on the 2m band with a device the size of a packet of cigarettes with
no external aerial and a single AA battery.

On the one hand, that makes paging pretty insecure: it's all broadcast in plaintext, and 
an appropriate radio would trivially pick up all pages (warning: might be illegal under the 1948
Wireless Telegraphy Act, consult a lawyer before firing up your GNU Radio hardware).

On the other hand, that means the devices themselves are essentially untrackable: you
could at very close range possibly locate an individual device by faking a page
addressed to it and then looking for TEMPEST emissions from the receiver as it
responds to its coded address, but that doesn't seem a terribly practical or useful
approach: in reality, any page wakes up all pagers.


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