The way they describe it, they send light down a cable, then watch for
   the reflection to come back to them.
   The reflection should look the same with every single pulse of light,
   unless something affects it, which in this case would be the vibrations
   of sound.
   So it should pick up sound along the entire length of cable, which
   would return a lot of ambient noise if you're trying to hear inside
   someone's house from all the way back at a utility company.
   I don't know how good their audio filtering abilities are, but it seems
   like wherever you take measurements can't be too far from what you want
   to hear.

   On Thu, Jun 16, 2016 at 1:56 PM, This 1s <[1]this1s@mailbox.org> wrote:

   Looking for stuff I found this post:

   [2]http://blogs.wsj.com/tech-europe/2012/09/04/turning-a-fiber-optic-ca
   ble-into-a-microphone/

   Is internet cable in house a hot mic?

   Is it the end of the fiber, the field around the cable, or both?

   Thanks in advance :D

References

   1. mailto:this1s@mailbox.org
   2. http://blogs.wsj.com/tech-europe/2012/09/04/turning-a-fiber-optic-cable-into-a-microphone/