Tiny gravity sensor could detect drug tunnels, mineral deposits By Sid PerkinsMar. 30, 2016 , 1:00 PM A new device the size of a postage stamp can detect 1-part-per-billion changes in Earth’s gravitational field—equivalent to what the gizmo would experience if it were lifted a mere 3 millimeters. The technology may become so cheap and portable it could one day be mounted on drones to spot everything from hidden drug tunnels to valuable mineral deposits. Gravity’s force is nearly the same everywhere on Earth. But there can be minute fluctuations, based on the density of the rock or other material...