Secret network

[Matthew J Ghio <mg5n+@andrew.cmu.edu>]

There is something else that we can use for secret communications and
that is ...  (don't laugh, I'm serious) - water pipes.  Many places
still use metal pipes, thru which radio waves can travel quite well.  I
read an article in a science magazine a few weeks ago, where a team of
researchers were tracking various electromagnetic emissions in
residential households.  They fould that a lot of background magnetic
fields and radio emissions were coming from the water pipes.  When the
neighbors used certain appliances, they could detect it because the EM
emmissions were picked up and carried by the metal water pipes.  And
that's was just background noise.  Imagine what we could transmit by
intentionally broadcasting signals thru the metal pipes!  Also, most of
the "noise" was low frequency, and since our transmitters would be high
frequency, it would probably work pretty well (unless, of course, you
had plastic pipes).  Most of the local net traffic could be handled thru
the pipe-network, while the radio transmitters, lasers & microwave stuff
could be used for longer distance stuff.