Beepers can also be used to track you down!

[karn@qualcomm.com (Phil Karn)]

Eh? Conventional pocket pagers are receive only. This is well known. Oh,
they probably do emit tiny amounts of RF from their local oscillators,
but I doubt much could be done with that.

Cell phones, on the other hand, *do* tell the system which cell you
are in, and they can do this even when you're not in a call. It's
called "registration".  The usual purpose is benign: directing pages
(land-to-mobile call requests) only to the cell you're in, instead of
having to "flood" them all over the system. But it *could* be used to
keep track of your location.

I carry both a pager and a cell phone.  Normally I keep the cell phone
turned off to save its batteries. When I get a page, I can turn the
phone on and return the call.  The pager/cellphone combination is very
nice, as I effectively get "caller ID" functionality.  Even better,
*I* get to choose when, how or even if to answer a particular page.
And since pagers are unidirectional (no acks) I can always lie about
not having gotten a page from somebody I don't want to talk to!  :-)

Phil