Engineers at the University of Arizona College of Engineering are testing a UK-developed monitoring system that could be used to watch the border between the US and Mexico continuously.

The border-monitoring system known as Helios consists of fibre-optic cables, lasers and detectors. More accurately described as a distributed acoustic sensor, it relies on the phenomenon of optical backscattering for its operation and is made by British company Fotech Solutions .

In use, the system transmits laser pulses through fibre-optic cables buried in the ground. The small vibrations caused by a moving object on the surface above hit the fibre-optic cables, slightly distorting them. The distortion creates a unique signature change in the laser pulses, which can be detected by a Helios detector at one, or both, ends of the cable.