Underground security system
An underground surveillance system could watch the entire US-Mexico border continuously.
The border-monitoring system, known as Helios, consists of laser pulses transmitted through fiber-optic cables buried in the ground that respond to movements on the surface above. A detector at one or both ends of the cable analyzes these responses.
Helios is sensitive enough to detect a dog and can discriminate between people, horses and trucks. The system can avoid being triggered by small animals, and can also tell if people are running or walking, or digging, and in which direction, said researchers at The University of Arizona College of Engineering.