The typical smartphone user can give off a total of nearly 100 pieces of highly technical data through calls, texts and other activities, according to research by Tracy Ann Kosa, a digital-privacy expert at the University of Ontario. This information includes the time that phones make contact with cellphone towers, the direction of the tower with respect to the phone and the signal strength at the time…

A cat-and-mouse game has evolved, with terror suspects frequently swapping SIM cards, or phone identification cards, to confuse intelligence agencies, former officials said. The U.S. has countered by devising how to monitor the phone and the SIM card separately.

“You keep pulling the thread. It’s critical stuff,” one former senior intelligence official said. “In every major terrorist operation or capture operation, metadata has played a huge role.”

Some of the most important metadata, cellphone location information, varies depending on the area covered by a cell tower. In rural areas, one tower may serve wide swaths of territory, but in urban areas, towers are more targeted.