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Product: Fence
Breach Detection   (+4)  [vote for, against]
Infallible fence

In the movies, military compounds often get broken into by cunning individuals who snip a convenient hole in the chicken-wire fence.

These intruders could easily be detected through the application of DSP. A device at one end of the fence would transmit an electrical impulse or sweep signal into the metal structure, and listen for the echoes both transmitted and reflected. Even a single snip into the wire mesh structure would alter the received signal, which in many cases, perhaps through iterative reconstruction, could pinpoint its exact location.

This seems like something that would already have been invented, but all I could find were vibration-detection systems which involve attaching extra sensors to the fence.
-- mitxela, Oct 03 2019

Senstar FlexZone Locating Fence-Mounted Intrusion Detection Sensor https://bulldogfire...n-detection-sensor/
Mentioned in my anno. A TDR-based system that "detects and locates any attempt to cut, scale, or somehow get through a fence", locating the intrusion to within 3 m. [notexactly, Oct 03 2019]

Southwest Microwave Intrepid MicroPoint II Fence Detection System [PDF] http://www.southwes...I-Data-Sheet-EN.pdf
Mentioned in my anno. A system "using proprietary Digital Signal Processing (DSP) algorithms to precisely locate intrusion attempts to within 3 meters (10 ft) while ignoring harmless disturbances caused by wind, rain or vehicle traffic". Also runs its power and communications over the same cables. Can have sensitivity set individually for each 1.1-meter section of fence. [notexactly, Oct 03 2019]

Future Fibre Technologies: The Boundaries of Security [PDF DL] https://www.git-sec...m/file/track/3066/1
Mentioned in my anno. See page 30 for a description of the special coax-with-sense-wires-in-keyways cable. [notexactly, Oct 04 2019]

This is definitely Baked but possibly not WKTE (for obvious reasons). Systems certainly existed and were deployed as early as 1993.
-- 8th of 7, Oct 03 2019

Did you use the term 'time-domain reflectometry' in your searching?
-- notexactly, Oct 03 2019

Some previous colleagues of mine have been deploying this kind of system, and closely-related fibre-acoustic systems in undisclosed locations since about 2008.
-- Frankx, Oct 03 2019

Sorry, that sounded like I was dissing the idea, I’m not. It’s a very good idea! [+] but there are implementations, not widely known, that do exist.
-- Frankx, Oct 03 2019

Curse my spelling! Before opening, I was imagining all sorts of ways of tracking in utero baby position ... and pinging when correct position closest to predicted birth date...
To avoid false triggers, wouldn't the sensors have to be quite close together, and the tension maintained in the wire (which expands in summer/contracts in winter)? <pops along to Area 51, to see how they might do it>
-- Dub, Oct 03 2019

A quick Google search for [ tdr fence intrusion detection ] turns up several relevant pages and PDF documents. These systems seem to typically use real cable instead of sending the signal directly through the fence, and they can detect people climbing the fence, not just cutting through it! See [links] for details.

Another relevant search term turns out to be Perimeter Intrusion Detection System (PIDS).
-- notexactly, Oct 03 2019

Baked, and commonplace.
-- xenzag, Oct 04 2019

The nearest I can think of is the Fibre Bragg Grating sensor, where the frequency of light reflected varies with strain, temperature etc.
-- Frankx, Oct 04 2019

random, halfbakery