Phone surveillance experts with the organization’s Operational Technology Resources (OTTER) unit, they were installed—Trey preferred to say shit-pitted—in a basement sublevel some two hundred feet below the administrative section where Carol Morse, Leo Harris and more of the big wheels were officed. With renovations to the warehouse still incomplete, their work space was only reachable by creaking, archaic early-twentieth-century freight elevators and plunging, claustrophobic stairwells...but its equipment and systems were state of the art.

Raymore jumped out of his seat, hurried over to Castro’s station and looked at her map screen. It really didn’t look a bit different from his or any other conventional GPS-based navigational map. But what made it very different was the unconventional software beneath its digital hood.

Tracking a mobile phone with the Global Positioning System was old hat. Cellular towers received signals from GPS satellites, which in turn retransmitted those signals to phones within range. The phone’s location could be determined by triangulating its position relative to those towers. As its user moved away from one set of towers and within range of another, his or her movements could be followed on a map.

But turn off the phone and the job got stickier. When a phone was powered off, it did not receive cellular signals, and GPS tracking didn’t work, period.

Needlefish, however, did not need GPS to track a phone. It did not require cellular data to work. Instead, it employed a far more complex and sophisticated side-channel method that interpreted readings from sensor arrays inside the phone.

Mobile devices were jam-packed with them. Every phone had a gyroscope, thermometer sensors, a magnetometer, an accelerometer, a proximity sensor, touch-screen sensors, ambient-light sensors and as many as four microphones, to name a bunch. These sensors might rest, but they never slept. The gyro was an exceptionally busy little bugger. A phone’s compass app relied on it to provide directions. Also, the gyro—along with the accelerometer, which measured the speed of a phone’s movement—was responsible for rotating a screen image whenever someone changed its orientation...say, to watch a video horizontally in landscape mode.

This pair of sensors—accelerometer and gyroscope—were Needlefish’s embedded moles inside a phone. By accessing its compass app through an installed code, it could detect whether the phone moved a few degrees right or left, or up or down. The technology itself wasn’t new. It had been around for about a decade. But years of advances in the field of artificial intelligence had been needed before it could be used to actually pinpoint a phone’s whereabouts.