"These geolocation capabilities can expose personal information, locations, routines, and numbers of DOD personnel, and potentially create unintended security consequences and increased risk to the joint force and mission," a memo obtained by the Associated Press said. It's up to ranking officers in less-sensitive areas to decide whether their charges can use GPS functions, based on the threat level in that location. The Defense Department will also provide training on the risks that fitness trackers bring.

Earlier this year, it emerged that fitness app Strava was exposing the location of US bases through publicly visible heatmaps that showed user activity. Soldiers were sharing their workout routes, which contributed to the data that Strava used for the heatmaps, and the Pentagon unsurprisingly was concerned. Strava has since restricted access to the heatmaps. In May, the Pentagon banned Huawei and ZTE phones from military base retailers, partly over concerns that the Chinese government could order the companies to track soldiers' movements.