Apparently the Drug Enforcement Administration operates a 'Central Tracking System' through which "all DEA assets and investigative targets" are monitored in real time and historically.

The information appears in a DEA request for information about GPS monitoring systems posted on the Federal Business Opportunities website in late February 2015. The request specifies that DEA is interested in learning about the most current GPS tracking technology capable of sending information to a remote server and establishing 'geofences', among other capabilities. The DEA wants to know about devices no larger than 4.7" x 2.8" x 1.75" and weighing less than two pounds.