[VW]

The GPS satellites have no way of knowing whether a GPSr is receiving their signal or not, because the GPSr is a receiver only. A BT GPSr then takes that signal and transmits it to a device such as a WM device. There is no addressing at all. It operates basically via triangulation (quadrangulation?) at a large scale. Thats why generally the more satellites your GPSr receivers the better the accuracy will be.

They do make BT GPS loggers that operate as a BT GPS but also logs where you have been so theoretically you could buy one of those, throw it in her backpack and see where she has been all day after the fact