If you want to monitor physical borders, such as walls and fences, a fiber-optic sensing system is ideal as they enable you to measure sound, movement or temperature – continuously and in real-time – along with long structures.
For remote borders with little or no infrastructure, there are various techniques that can keep an eye, or rather an ear, out. QinetiQ, a British firm, has a system called OptaSense, which uses a fiber-optic cable laid in the ground. Sound from above creates vibrations in this cable.
Fiber optic sensing technology converts cables installed alongside transport infrastructure, such as railroads or highways, into an array of thousands of sensors which can detect acoustics, temperature or strain signals by using optical sensing techniques.
"Our approach has always been that when fiber-optic sensing is used, it's usually one of many other solutions," Mark Uncapher, the director of the Fiber Optic Sensing Association, told INSIDER.